American intervention 1965
127-400: 1966 1967 Tet Offensive and aftermath Vietnamization 1969–1971 1972 Post- Paris Peace Accords (1973–1974) Spring 1975 Air operations Naval operations Lists of allied operations PIRAZ is a United States Navy acronym for Positive Identification Radar Advisory Zone . The zone is defined by the air search radar coverage of a ship patrolling
254-696: A U.S. Special Forces border outpost at Lộc Ninh , in Bình Long Province . This attack sparked a ten-day battle that drew in elements of the U.S. 1st Infantry Division and the ARVN 18th Division and left 800 PAVN troops dead at its conclusion. The most severe of what came to be known as "the Border Battles" erupted during October and November around Dak To , another border outpost in Kon Tum Province . The clashes there between
381-567: A U.S. bombing raid on COSVN after having been evacuated from Cambodia. After cementing their position during the Party crackdown, the militants sped up planning for a major conventional offensive to break the military deadlock. They concluded that the Saigon government and the U.S. presence were so unpopular with the population of the South that a broad-based attack would spark a spontaneous uprising of
508-426: A central point, or perhaps to a distributed system in which all participate, such that the information can be correlated and a location computed. Modern SIGINT systems, therefore, have substantial communications among intercept platforms. Even if some platforms are clandestine, there is still a broadcast of information telling them where and how to look for signals. A United States targeting system under development in
635-449: A compromise: The CIA would drop its insistence on including the irregulars in the final tally of forces and add a prose addendum to the estimate that would explain the agency's position. George Allen, Carver's deputy, laid responsibility for the agency's capitulation at the feet of Richard Helms , the director of the CIA. He believed that "it was a political problem ... [Helms] didn't want
762-472: A confirmation, followed by observation of artillery fire, may identify an automated counterbattery fire system. A radio signal that triggers navigational beacons could be a radio landing aid for an airstrip or helicopter pad that is intended to be low-profile. Patterns do emerge. A radio signal with certain characteristics, originating from a fixed headquarters, may strongly suggest that a particular unit will soon move out of its regular base. The contents of
889-615: A conventional conflict might draw China in, as had happened in the Korean War . They also resisted the idea of negotiating with the allies. Moscow, on the other hand, advocated negotiations, but simultaneously armed Hanoi's forces to conduct a conventional war on the Soviet model. North Vietnamese foreign policy therefore consisted of maintaining a critical balance between war policy, internal and external policies, domestic adversaries, and foreign allies with "self-serving agendas." To "break
1016-609: A countrywide assault on the cities, conducted primarily by VC forces. Concurrently, a propaganda offensive to induce ARVN troops to desert and the South Vietnamese population to rise up against the government would be launched. If outright victory was not achieved, the battle might still lead to the creation of a coalition government and the withdrawal of the Americans. If the general offensive failed to achieve these purposes, follow-up operations would be conducted to wear down
1143-406: A dawning realization that if current trends continued, Hanoi would eventually lack the resources necessary to affect the military situation in the South. As a result, there were more strident calls by the moderates for negotiations and a revision of strategy. They felt that a return to guerrilla tactics was more appropriate since the U.S. could not be defeated conventionally. They also complained that
1270-611: A designated PIRAZ station. The concept was similar to radar picket stations established in World War II. The PIRAZ ship requires a Naval Tactical Data System radio-linked computer installation to effectively identify and track all aircraft anticipated to enter the airspace of the zone during combat. The concept originated in the summer of 1966 as Yankee station was established for United States Task Force 77 aircraft carriers launching strikes against North Vietnam . A fixed patrol station within range of land-based aircraft made
1397-458: A different ECCM way to identify frequencies not being jammed or not in use. The earliest, and still common, means of direction finding is to use directional antennas as goniometers , so that a line can be drawn from the receiver through the position of the signal of interest. (See HF/DF .) Knowing the compass bearing, from a single point, to the transmitter does not locate it. Where the bearings from multiple points, using goniometry, are plotted on
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#17327809523671524-640: A lower level, German cryptanalysis, direction finding, and traffic analysis were vital to Rommel's early successes in the Western Desert Campaign until British forces tightened their communications discipline and Australian raiders destroyed his principle SIGINT Company. The United States Department of Defense has defined the term "signals intelligence" as: Being a broad field, SIGINT has many sub-disciplines. The two main ones are communications intelligence (COMINT) and electronic intelligence (ELINT). A collection system has to know to look for
1651-668: A major North Vietnamese military buildup. In addition to captured documents (a copy of Resolution 13 , for example, was captured by early October), observations of enemy logistical operations were also quite clear: in October, the number of trucks observed heading south through Laos on the Hồ Chí Minh Trail jumped from the previous monthly average of 480 to 1,116. By November this total reached 3,823 and, in December, 6,315. On 20 December, Westmoreland cabled Washington that he expected
1778-407: A map, the transmitter will be located at the point where the bearings intersect. This is the simplest case; a target may try to confuse listeners by having multiple transmitters, giving the same signal from different locations, switching on and off in a pattern known to their user but apparently random to the listener. Individual directional antennas have to be manually or automatically turned to find
1905-648: A particular signal. "System", in this context, has several nuances. Targeting is the process of developing collection requirements : First, atmospheric conditions, sunspots , the target's transmission schedule and antenna characteristics, and other factors create uncertainty that a given signal intercept sensor will be able to "hear" the signal of interest, even with a geographically fixed target and an opponent making no attempt to evade interception. Basic countermeasures against interception include frequent changing of radio frequency , polarization , and other transmission characteristics. An intercept aircraft could not get off
2032-515: A peace-time codebreaking agency should be created. The Government Code and Cypher School (GC&CS) was the first peace-time codebreaking agency, with a public function "to advise as to the security of codes and cyphers used by all Government departments and to assist in their provision", but also with a secret directive to "study the methods of cypher communications used by foreign powers". GC&CS officially formed on 1 November 1919, and produced its first decrypt on 19 October. By 1940, GC&CS
2159-523: A precise picture of the normal operation of the High Seas Fleet , to infer from the routes they chose where defensive minefields had been placed and where it was safe for ships to operate. Whenever a change to the normal pattern was seen, it immediately signalled that some operation was about to take place, and a warning could be given. Detailed information about submarine movements was also available. The use of radio-receiving equipment to pinpoint
2286-423: A preliminary phase, during which diversionary attacks would be launched in the border areas of South Vietnam to draw American attention and forces away from the cities. The general offensive and uprising would then commence with simultaneous actions on major allied bases and most urban areas, and with particular emphasis on the cities of Saigon and Huế. Concurrently, a substantial threat would have to be made against
2413-419: A protracted war of attrition". In May, MACV attempted to obtain a compromise from the CIA by maintaining that VC militias did not constitute a fighting force but were essentially low-level fifth columnists used for information collection. With the groups deadlocked, George Carver, CIA Special Assistant for Vietnam Affairs, represented the CIA in the last stage of the negotiations. In September, Carver devised
2540-401: A radar is operating. Once the radar is known to be in the area, the next step is to find its location. If operators know the probable frequencies of transmissions of interest, they may use a set of receivers, preset to the frequencies of interest. These are the frequency (horizontal axis) versus power (vertical axis) produced at the transmitter, before any filtering of signals that do not add to
2667-401: A safe distance from the user of the transmitter. When locations are known, usage patterns may emerge, from which inferences may be drawn. Traffic analysis is the discipline of drawing patterns from information flow among a set of senders and receivers, whether those senders and receivers are designated by location determined through direction finding , by addressee and sender identifications in
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#17327809523672794-404: A sensor is unique. MASINT then becomes more informative, as individual transmitters and antennas may have unique side lobes, unintentional radiation, pulse timing, etc. Network build-up , or analysis of emitters (communication transmitters) in a target region over a sufficient period of time, enables creation of the communications flows of a battlefield. COMINT ( com munications int elligence)
2921-611: A series of coups had characterized the preceding years. Protests, campaigning and the atmosphere of elections were interpreted by the Politburo of the Communist Party of Vietnam and Lê Duẩn as signs that the population would embrace a 'general uprising' against the government of South Vietnam. The Politburo sought to exploit perceived instability and maintain political weakness in South Vietnam. During late 1967,
3048-426: A tactical SIGINT requirement, whereas the larger aircraft tend to be assigned strategic/national missions. Before the detailed process of targeting begins, someone has to decide there is a value in collecting information about something. While it would be possible to direct signals intelligence collection at a major sports event, the systems would capture a great deal of noise, news signals, and perhaps announcements in
3175-478: A tank battalion or tank-heavy task force. Another set of transmitters might identify the logistic net for that same unit. An inventory of ELINT sources might identify the medium - and long-range counter-artillery radars in a given area. Signals intelligence units will identify changes in the EOB, which might indicate enemy unit movement, changes in command relationships, and increases or decreases in capability. Using
3302-411: A vehicle. If these are regular reports over a period of time, they might reveal a patrol pattern. Direction-finding and radio frequency MASINT could help confirm that the traffic is not deception. The EOB buildup process is divided as following: Separation of the intercepted spectrum and the signals intercepted from each sensor must take place in an extremely small period of time, in order to separate
3429-529: A very public debate over military strategy took place in print and via radio between Thanh and his rival for military power, Giáp. Giáp had advocated a defensive, primarily guerrilla strategy against the U.S. and South Vietnam. Thanh's position was that Giáp and his adherents were centered on their experiences during the First Indochina War and that they were too "conservative and captive to old methods and past experience... mechanically repeating
3556-448: A winter-spring offensive during 1968 had begun in early 1967 and continued until early the following year. According to American sources, there has been an extreme reluctance among Vietnamese historians to discuss the decision-making process that led to the general offensive and uprising , even decades after the event. In official Vietnamese literature, the decision to launch the Tet offensive
3683-578: Is Amplitude comparison . An alternative to tunable directional antennas or large omnidirectional arrays such as the Wullenweber is to measure the time of arrival of the signal at multiple points, using GPS or a similar method to have precise time synchronization. Receivers can be on ground stations, ships, aircraft, or satellites, giving great flexibility. A more accurate approach is Interferometer. Modern anti-radiation missiles can home in on and attack transmitters; military antennas are rarely
3810-417: Is a sub-category of signals intelligence that engages in dealing with messages or voice information derived from the interception of foreign communications. COMINT is commonly referred to as SIGINT, which can cause confusion when talking about the broader intelligence disciplines. The US Joint Chiefs of Staff defines it as "Technical information and intelligence derived from foreign communications by other than
3937-415: Is acquired by a given country. Knowledge of physics and electronic engineering further narrows the problem of what types of equipment might be in use. An intelligence aircraft flying well outside the borders of another country will listen for long-range search radars, not short-range fire control radars that would be used by a mobile air defense. Soldiers scouting the front lines of another army know that
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4064-543: Is in the general area of the signal. The owner of the transmitter can assume someone is listening, so might set up tank radios in an area where he wants the other side to believe he has actual tanks. As part of Operation Quicksilver , part of the deception plan for the invasion of Europe at the Battle of Normandy , radio transmissions simulated the headquarters and subordinate units of the fictitious First United States Army Group (FUSAG), commanded by George S. Patton , to make
4191-610: Is the truncated version of the Lunar New Year festival name in Vietnamese, Tết Nguyên Đán , with the offense chosen during a holiday period as most ARVN personnel were on leave. The purpose of the wide-scale offensive by the Hanoi Politburo was to trigger political instability in a belief that mass armed assault on urban centers would trigger defections and rebellions . The offensive was launched prematurely in
4318-511: Is usually encrypted , signals intelligence may necessarily involve cryptanalysis (to decipher the messages). Traffic analysis —the study of who is signaling to whom and in what quantity—is also used to integrate information, and it may complement cryptanalysis. Electronic interceptions appeared as early as 1900, during the Boer War of 1899–1902. The British Royal Navy had installed wireless sets produced by Marconi on board their ships in
4445-407: The 1967 South Vietnamese presidential election , looked increasingly stable. Rivalries between South Vietnam's generals were becoming less chaotic, and Thiệu and Kỳ formed a joint ticket for the election. Despite efforts by North Vietnam to disrupt elections, higher than usual turnouts saw a political turning point towards a more democratic structure and ushered in a period of political stability after
4572-510: The Admiralty ; Room 40 . An interception service known as 'Y' service , together with the post office and Marconi stations, grew rapidly to the point where the British could intercept almost all official German messages. The German fleet was in the habit each day of wirelessing the exact position of each ship and giving regular position reports when at sea. It was possible to build up
4699-527: The Battle of Jutland as the British fleet was sent out to intercept them. The direction-finding capability allowed for the tracking and location of German ships, submarines, and Zeppelins . The system was so successful that by the end of the war, over 80 million words, comprising the totality of German wireless transmission over the course of the war, had been intercepted by the operators of the Y-stations and decrypted. However, its most astonishing success
4826-521: The Demilitarized Zone (DMZ). The intense shelling (100–150 rounds per day) prompted Westmoreland to launch Operation Neutralize , an intense aerial bombardment campaign of 4,000 sorties into and just north of the DMZ. On 27 October, an ARVN battalion at Sông Bé , the capital of Phước Long Province , came under attack by an entire PAVN regiment. Two days later, another PAVN regiment attacked
4953-512: The People's Republic of China and called for the reunification of the nation by military means and that no negotiations should be undertaken with the Americans. This group was led by Communist Party First Secretary Lê Duẩn and Lê Đức Thọ (no relation). From the early to mid-1960s, the militants had dictated the direction of the war in South Vietnam. General Nguyễn Chí Thanh , the head of Central Office for South Vietnam (COSVN), headquarters for
5080-803: The Philippines for minor repairs and missile firing exercises before returning to the PIRAZ station. The ship would typically return to a United States home port for approximately six months after three PIRAZ station assignments with two intervening relief periods. The PIRAZ ship Combat Information Center (or CIC) was continuously staffed by 35 to 40 officers and sailors watching radar displays, updating position and identification information for NTDS computers, and maintaining radio communication with aircraft and other ships. Some CIC personnel acted as air traffic controllers providing either advisory control or close control. Close (or positive) control occurred when
5207-716: The Russian Army ’s advance early in World War I and led to their disastrous defeat by the Germans under Ludendorff and Hindenburg at the Battle of Tannenberg . In 1918, French intercept personnel captured a message written in the new ADFGVX cipher , which was cryptanalyzed by Georges Painvin . This gave the Allies advance warning of the German 1918 Spring Offensive . The British in particular, built up great expertise in
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5334-548: The Son Tay Raid on 21 November 1970. PIRAZ ships carried long-range RIM-2 Terrier or RIM-8 Talos surface-to-air missiles to defend their stations. Chicago fired RIM-8H Talos-ARM anti-radar homing missiles against North Vietnamese shore-based radar stations. Each PIRAZ ship was accompanied on station by a "shotgun" torpedo boat destroyer with quick-firing guns to defend the PIRAZ ships from torpedo boat attack. PIRAZ ships provided protective radar surveillance of
5461-521: The remotely piloted vehicles performing aerial photo reconnaissance of North Vietnam. As the Gulf of Tonkin PIRAZ station routine developed, a PIRAZ ship would typically remain on station for approximately 30 days before being relieved by another ship. During the 30-day relief period, the ship would usually travel to a liberty port in Hong Kong or Japan and then to the U.S. Naval Base Subic Bay in
5588-610: The 14th Plenary session of the Party Central Committee in January 1968. The resultant Resolution 14 was a major blow to domestic opposition and "foreign obstruction". Concessions had been made to the center group, however, by agreeing that negotiations were possible, but the document essentially centered on the creation of "a spontaneous uprising in order to win a decisive victory in the shortest time possible." Contrary to Western belief, Giáp did not plan or command
5715-582: The American public still disapproved of the President's handling of the war. The American public, "more confused than convinced, more doubtful than despairing ... adopted a 'wait and see' attitude." During a discussion with an interviewer from Time magazine, Westmoreland dared the communists to launch an attack: "I hope they try something because we are looking for a fight." Planning in Hanoi for
5842-554: The Americans would win the war. There was a discrepancy, however, between the order of battle estimates of the MACV and the Central Intelligence Agency (CIA) concerning the strength of VC guerrilla forces within South Vietnam. In September, members of the MACV intelligence services and the CIA met to prepare a Special National Intelligence Estimate that would be used by the administration to gauge U.S. success in
5969-548: The COMINT gathering method enables the intelligence officer to produce an electronic order of battle by traffic analysis and content analysis among several enemy units. For example, if the following messages were intercepted: This sequence shows that there are two units in the battlefield, unit 1 is mobile, while unit 2 is in a higher hierarchical level, perhaps a command post. One can also understand that unit 1 moved from one point to another which are distant from each 20 minutes with
6096-508: The Communist Party militants. For the moderates and centrists, it offered the prospect of negotiations and a possible end to the American bombing of the North. Only in the eyes of the militants, therefore, did the offensive become a "go for broke" effort. Others in the Politburo were willing to settle for a much less ambitious "victory". The PAVN official history states that the objectives of
6223-438: The German defense think that the main invasion was to come at another location. In like manner, fake radio transmissions from Japanese aircraft carriers, before the Battle of Pearl Harbor , were made from Japanese local waters, while the attacking ships moved under strict radio silence. Traffic analysis need not focus on human communications. For example, a sequence of a radar signal, followed by an exchange of targeting data and
6350-680: The January–February 1968 offensive, but it can also include the so-called " Mini-Tet " offensive that took place in May and the Phase III offensive in August, or the 21 weeks of unusually intense combat that followed the initial attacks in January. Leading up to the Tet Offensive were years of marked political instability and a series of coups after the 1963 South Vietnamese coup . In 1966,
6477-476: The North Vietnamese had done was carry out the first stage of their plan: to fix the attention of the U.S. command on the borders and draw the bulk of U.S. forces away from the heavily populated coastal lowlands and cities. Westmoreland was more concerned with the situation at Khe Sanh, where, on 21 January 1968, a force estimated at 20,000–40,000 PAVN troops had besieged the U.S. Marine garrison. MACV
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#17327809523676604-531: The PAVN/VC "to undertake an intensified countrywide effort, perhaps a maximum effort, over a relatively short period of time." Despite all the warning signs, however, the allies were still surprised by the scale and scope of the offensive. According to ARVN Colonel Hoang Ngoc Lung the answer lay with the allied intelligence methodology itself, which tended to estimate the enemy's probable course of action based upon their capabilities, not their intentions. Since, in
6731-430: The PIRAZ ship. PIRAZ shipboard air controllers would also provide positive control for aircraft requiring in-flight refueling. Gulf of Tonkin barrier CAP (BARCAP) routinely refueled; and CAP involved in an engagement usually returned with a low fuel state requiring emergency refueling. Three Chicago AICs assisted 52 declared emergency refueling situations for Air Force aircraft in a single day. Preferred procedure turns
6858-599: The Russian fleet prepared for conflict with Japan in 1904, the British ship HMS Diana stationed in the Suez Canal intercepted Russian naval wireless signals being sent out for the mobilization of the fleet, for the first time in history. Over the course of the First World War , a new method of signals intelligence reached maturity. Russia’s failure to properly protect its communications fatally compromised
6985-457: The South, was another prominent militant. The followers of the Chinese line centered their strategy against the U.S. and its allies on large-scale, main force actions rather than the protracted guerrilla war espoused by Mao Zedong . By 1966–1967, however, after suffering massive casualties, stalemate on the battlefield, and destruction of the northern economy by U.S. aerial bombing , there was
7112-547: The Tet casualties and the escalation of draft calls. Subsequently, the Johnson Administration sought negotiations to end the war. Shortly before the 1968 United States presidential election , Republican candidate and former vice president Richard Nixon encouraged South Vietnamese President Nguyễn Văn Thiệu to become publicly uncooperative in the negotiations, casting doubt on Johnson's ability to bring peace. The term "Tet offensive" usually refers to
7239-483: The Tet offensive were to: annihilate and cause the total disintegration of the bulk of the puppet army, overthrow the "puppet" (South Vietnamese) regime at all administrative levels, and place all government power in the hands of the people. Annihilate a significant portion of the American military's troop strength and destroy a significant portion of his war equipment in order to prevent the American forces from being able to carry out their political and military missions; on
7366-491: The Thiệu government in the southern press. Launching such an offensive would also finally put an end to what had been described as "dovish calls for talks, criticism of military strategy, Chinese diatribes of Soviet perfidy, and Soviet pressure to negotiate—all of which needed to be silenced." In October, the Politburo decided on the Tet holiday as the launch date and met again in December to reaffirm its decision and formalize it at
7493-792: The Tonkin Gulf PIRAZ station, successful AICs concentrated on providing threat information, collecting and sorting tactical information as it developed, and informing the Combat Air Patrols (or CAP) about the threat location and activities while letting aircrews deal with bearing drift and controlling their headings. Ships on PIRAZ station mounted the air search radar closest to enemy airfields and were best positioned to offer radar information to Navy, Air Force, and Marine Corps fighters. Combat Air Patrols (CAP) were typically under advisory control, and would come under positive control when being vectored to hostile aircraft detected by
7620-457: The U.S. Khe Sanh Combat Base . The Khe Sanh actions would draw PAVN forces away from the offensive into the cities, but Giáp considered them necessary to protect his supply lines and divert American attention. Attacks on other U.S. forces were of secondary, or even tertiary importance, since Giáp considered his main objective to be weakening or destroying the South Vietnamese military and government through popular revolt. The offensive, therefore,
7747-617: The U.S. command in Saigon was perplexed by a series of actions initiated by the PAVN/VC in the border regions. On 24 April a U.S. Marine Corps patrol prematurely triggered a PAVN offensive aimed at taking Khe Sanh Combat Base, the western anchor of the Marines' defensive positions in Quảng Trị Province . For 49 days during early September and lasting into October, the PAVN began shelling the U.S. Marine outpost of Con Thien , just south of
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#17327809523677874-593: The U.S. perspective was summed up by an MACV intelligence analyst: "If we'd gotten the whole battle plan, it wouldn't have been believed. It wouldn't have been credible to us." The Tet offensive would later be used in a textbook at West Point as an example of "an allied intelligence failure to rank with Pearl Harbor in 1941 or the Ardennes offensive in 1944." Lieutenant Colonel Dave R. Palmer: Current Readings in Military History . From early to late 1967,
8001-457: The VC with new AK-47 assault rifles and B-40 rocket-propelled grenade launchers, which granted them superior firepower over the ARVN. To pave the way and to confuse the allies as to its intentions, Hanoi launched a diplomatic offensive. Foreign Minister Trinh announced on 30 December that Hanoi would rather than could open negotiations if the U.S. unconditionally ended Operation Rolling Thunder ,
8128-581: The VC. General Bruce Palmer Jr. , one of Westmoreland's three Field Force commanders, claimed that "the Viet Cong has been defeated" and that "He can't get food and he can't recruit. He has been forced to change his strategy from trying to control the people on the coast to try to survive in the mountains." Westmoreland was even more emphatic in his assertions. At an address at the National Press Club on 21 November, he reported that, as of
8255-453: The actual information is at 800 kHz and 1.2 MHz. Real-world transmitters and receivers usually are directional. In the figure to the left, assume that each display is connected to a spectrum analyzer connected to a directional antenna aimed in the indicated direction. Spread-spectrum communications is an electronic counter-countermeasures (ECCM) technique to defeat looking for particular frequencies. Spectrum analysis can be used in
8382-486: The administration to launch a so-called "success offensive", a concerted effort to alter the widespread public perception that the war had reached a stalemate and to convince the American people that the administration's policies were succeeding. Under the leadership of National Security Advisor Walt W. Rostow , the news media then was inundated by a wave of effusive optimism. Every statistical indicator of progress, from "kill ratios" and "body counts" to village pacification,
8509-491: The agency ... contravening the policy interest of the administration." During the second half of 1967 the administration had become alarmed by criticism, both inside and outside the government, and by reports of declining public support for its Vietnam policies. According to public opinion polls, the percentage of Americans who believed that the U.S. had made a mistake by sending troops to Vietnam had risen from 25 percent in 1965 to 45 percent by December 1967. This trend
8636-402: The allied estimation, the communists hardly had the capability to launch such an ambitious enterprise: "There was little possibility that the enemy could initiate a general offensive, regardless of his intentions." The answer could also be partially explained by the lack of coordination and cooperation between competing intelligence branches, both South Vietnamese and American. The situation from
8763-484: The allied intelligence collection apparatus in Saigon. During the late summer and fall of 1967 both South Vietnamese and U.S. intelligence agencies collected clues that indicated a significant shift in communist strategic planning. By mid-December, mounting evidence convinced many in Washington and Saigon that something big was underway. During the last three months of the year intelligence agencies had observed signs of
8890-478: The attacks and inflicted heavy casualties on PAVN/VC forces. The popular uprising anticipated by Hanoi never materialized. During the Battle of Huế , intense fighting lasted for a month, resulting in the destruction of the city. During its occupation, the PAVN/VC executed thousands of people in the Massacre at Huế . Around the American combat base at Khe Sanh , fighting continued for two more months. The offensive
9017-497: The basis, crush the American will to commit aggression and force the United States to accept defeat in South Vietnam and end all hostile actions against North Vietnam. In addition, using this as the basis, they would achieve the immediate goals of the revolution, which were independence, democracy, peace, and neutrality in South Vietnam, and then move toward achieving peace and national unification. The operation would involve
9144-608: The best known PIRAZ air controllers of the Vietnam War. Chief Nowell provided air control information for more than 100 live engagements with enemy aircraft including 25 percent of intercepts leading to destruction of North Vietnamese fighters in 1972. In August 1972, Chief Nowell became the second enlisted man in Navy history to be awarded the Distinguished Service Medal . One PIRAZ shipboard air controller
9271-676: The bombing campaign against North Vietnam. This announcement provoked a flurry of diplomatic activity (which amounted to nothing) during the last weeks of the year. South Vietnamese and U.S. military intelligence estimated that PAVN/VC forces in South Vietnam during January 1968 totaled 323,000 men, including 130,000 PAVN regulars, 160,000 VC and members of the infrastructure, and 33,000 service and support troops. They were organized into nine divisions composed of 35 infantry and 20 artillery or anti-aircraft artillery regiments, which were, in turn, composed of 230 infantry and six sapper battalions. Signs of impending communist action were noticed among
9398-506: The broader organizational order of battle . EOB covers both COMINT and ELINT. The Defense Intelligence Agency maintains an EOB by location. The Joint Spectrum Center (JSC) of the Defense Information Systems Agency supplements this location database with five more technical databases: For example, several voice transmitters might be identified as the command net (i.e., top commander and direct reports) in
9525-419: The conflict. Provided with an enemy intelligence windfall accrued during Operations Cedar Falls and Junction City , the CIA members of the group believed that the number of VC guerrillas, irregulars, and cadre within the South could be as high as 430,000. The MACV Combined Intelligence Center, on the other hand, maintained that the number could be no more than 300,000. Westmoreland was deeply concerned about
9652-701: The controller provided specific altitudes, courses, and speeds to the pilot. Personnel providing positive control are called Air Intercept Controllers (AIC). Advisory control simply offered advice concerning proximity to operating area boundaries, nearby air traffic, or known Surface-to-air missile (SAM) or Anti-Aircraft Artillery (AAA) sites. Chicago' s CIC included a secret signals intelligence (Sigint) team using modern electronics to evaluate very weak electromagnetic radiations from North Vietnamese aircraft or SAM sites. The team could transfer real time Sigint information to PIRAZ air controllers. Chicago AICs monitored up to 50 North Vietnamese MiGs simultaneously. On
9779-446: The decision to target is made, the various interception points need to cooperate, since resources are limited. Knowing what interception equipment to use becomes easier when a target country buys its radars and radios from known manufacturers, or is given them as military aid . National intelligence services keep libraries of devices manufactured by their own country and others, and then use a variety of techniques to learn what equipment
9906-469: The different signals to different transmitters in the battlefield. The complexity of the separation process depends on the complexity of the transmission methods (e.g., hopping or time-division multiple access (TDMA)). By gathering and clustering data from each sensor, the measurements of the direction of signals can be optimized and get much more accurate than the basic measurements of a standard direction finding sensor. By calculating larger samples of
10033-429: The early morning hours of 30 January in large parts of the I and II Corps Tactical Zones of South Vietnam. This early attack allowed allied forces some time to prepare defensive measures. When the main operation began during the early morning hours of 31 January, the offensive was countrywide; eventually more than 80,000 PAVN/VC troops struck more than 100 towns and cities, including 36 of 44 provincial capitals, five of
10160-407: The economic viability of North Vietnam should come before support of a massive and conventional southern war and they generally followed the Soviet line of peaceful coexistence by reunifying Vietnam through political means. Heading this faction were party theorist Trường Chinh and Minister of Defense Võ Nguyên Giáp . The militant faction, on the other hand, tended to follow the foreign policy line of
10287-425: The end of 1967, the communists were "unable to mount a major offensive ... I am absolutely certain that whereas in 1965 the enemy was winning, today he is certainly losing...We have reached an important point when the end begins to come into view." By the end of the year the administration's approval rating had indeed crept up by eight percent, but an early January Gallup poll indicated that forty-seven percent of
10414-517: The enemy and lead to a negotiated settlement; Phase II was scheduled to begin on 5 May and Phase III on 17 August. Preparations for the offensive were already underway. The logistical build-up began in mid-year, and by January 1968, 81,000 tons of supplies and 200,000 troops, including seven complete infantry regiments and 20 independent battalions made the trip south on the Ho Chi Minh Trail . This logistical effort also involved re-arming
10541-559: The following month. Thanh was then ordered to the capital to explain his concept in person to the Military Central Commission. At a meeting in July, Thanh briefed the plan to the Politburo. On the evening of 6 July, after receiving permission to begin preparations for the offensive, Thanh attended a party and died of a heart attack after drinking too much. An alternative account is that Thanh died of injuries sustained in
10668-571: The four regiments of the PAVN 1st Division , the U.S. 4th Infantry Division , the 173rd Airborne Brigade and ARVN infantry and Airborne elements, lasted for 22 days. By the time the fighting was over, between 1,200 and 1,600 PAVN and 262 U.S. troops had been killed. MACV intelligence was confused by the possible motives of the North Vietnamese in prompting such large-scale actions in remote regions where U.S. artillery and aerial firepower could be applied indiscriminately, which meant that tactically and strategically, these operations made no sense. What
10795-512: The fronts, that we won the war!" Supreme Allied Commander, Dwight D. Eisenhower , at the end of the war, described Ultra as having been "decisive" to Allied victory. Official historian of British Intelligence in World War II Sir Harry Hinsley argued that Ultra shortened the war "by not less than two years and probably by four years"; and that, in the absence of Ultra, it is uncertain how the war would have ended. At
10922-420: The ground if it had to carry antennas and receivers for every possible frequency and signal type to deal with such countermeasures. Second, locating the transmitter's position is usually part of SIGINT. Triangulation and more sophisticated radio location techniques, such as time of arrival methods, require multiple receiving points at different locations. These receivers send location-relevant information to
11049-448: The information being transmitted. Received energy on a particular frequency may start a recorder, and alert a human to listen to the signals if they are intelligible (i.e., COMINT). If the frequency is not known, the operators may look for power on primary or sideband frequencies using a spectrum analyzer . Information from the spectrum analyzer is then used to tune receivers to signals of interest. For example, in this simplified spectrum,
11176-541: The late 1890s, and the British Army used some limited wireless signalling. The Boers captured some wireless sets and used them to make vital transmissions. Since the British were the only people transmitting at the time, the British did not need special interpretation of the signals that they were. The birth of signals intelligence in a modern sense dates from the Russo-Japanese War of 1904–1905. As
11303-541: The late 1990s, PSTS, constantly sends out information that helps the interceptors properly aim their antennas and tune their receivers. Larger intercept aircraft, such as the EP-3 or RC-135 , have the on-board capability to do some target analysis and planning, but others, such as the RC-12 GUARDRAIL , are completely under ground direction. GUARDRAIL aircraft are fairly small and usually work in units of three to cover
11430-534: The leadership in South Vietnam, represented by the Head of State Nguyễn Văn Thiệu and Prime Minister Nguyễn Cao Kỳ were persuaded to commit to democratic reforms in an effort to stabilize the political situation at a conference in Honolulu . Prior to 1967, the South Vietnamese constituent assembly was in the process of drafting a new constitution and eventual elections. The political situation in South Vietnam, after
11557-574: The location of any single transmitter was also developed during the war. Captain H.J. Round , working for Marconi , began carrying out experiments with direction-finding radio equipment for the army in France in 1915. By May 1915, the Admiralty was able to track German submarines crossing the North Sea. Some of these stations also acted as 'Y' stations to collect German messages, but a new section
11684-564: The message need not be known to infer the movement. There is an art as well as science of traffic analysis. Expert analysts develop a sense for what is real and what is deceptive. Harry Kidder , for example, was one of the star cryptanalysts of World War II, a star hidden behind the secret curtain of SIGINT. Generating an electronic order of battle (EOB) requires identifying SIGINT emitters in an area of interest, determining their geographic location or range of mobility, characterizing their signals, and, where possible, determining their role in
11811-410: The message, or even MASINT techniques for "fingerprinting" transmitters or operators. Message content other than the sender and receiver is not necessary to do traffic analysis, although more information can be helpful. For example, if a certain type of radio is known to be used only by tank units, even if the position is not precisely determined by direction finding, it may be assumed that a tank unit
11938-492: The newly emerging field of signals intelligence and codebreaking (synonymous with cryptanalysis). On the declaration of war, Britain cut all German undersea cables. This forced the Germans to communicate exclusively via either (A) a telegraph line that connected through the British network and thus could be tapped; or (B) through radio which the British could then intercept. Rear Admiral Henry Oliver appointed Sir Alfred Ewing to establish an interception and decryption service at
12065-501: The offensive himself. Thanh's original plan was elaborated on by a party committee headed by Thanh's deputy, Phạm Hùng , and then modified by Giáp. The Defense Minister may have been convinced to toe the line by the arrest and imprisonment of most of the members of his staff during the Revisionist Anti-Communist Party Affair. Although Giáp went to work "reluctantly, under duress", he may have found
12192-461: The other side will be using radios that must be portable and not have huge antennas. Even if a signal is human communications (e.g., a radio), the intelligence collection specialists have to know it exists. If the targeting function described above learns that a country has a radar that operates in a certain frequency range, the first step is to use a sensitive receiver, with one or more antennas that listen in every direction, to find an area where such
12319-517: The past." The arguments over domestic and military strategy also carried a foreign policy element, as North Vietnam, like South Vietnam, was largely dependent on outside military and economic aid. The vast majority of North Vietnam's military equipment was provided by either the Soviet Union or China. Beijing advocated that North Vietnam conduct a protracted war on the Maoist model, fearing that
12446-560: The policy of rejecting negotiations was in error. The Americans could only be worn down in a war of wills during a period of "fighting while talking". During 1967 things had become so bad on the battlefield that Lê Duẩn ordered Thanh to incorporate aspects of protracted guerrilla warfare into his strategy. During the same period, a counter-attack was launched by a new, third grouping (the centrists) led by President Hồ Chí Minh , Lê Đức Thọ, and Foreign Minister Nguyễn Duy Trinh , who called for negotiations. From October 1966 through April 1967,
12573-599: The population, which, if the offensive was successful, would enable the North Vietnamese to sweep to a quick, decisive victory. Their basis for this conclusion included: a belief that the South Vietnamese military was no longer combat-effective; the results of the 1967 presidential election (in which the Thiệu/Kỳ ticket had only received 24 percent of the popular vote); the Buddhist crises of 1963 and 1966 ; well-publicized anti-war demonstrations in Saigon; and continuous criticism of
12700-532: The position of the militants as Hanoi's strategy: the rejection of negotiations, the abandonment of protracted warfare, and the focus on the offensive in the towns and cities of South Vietnam. More arrests followed in November and December. The operational plan for the general offensive and uprising had its origin as the "COSVN proposal" at Thanh's southern headquarters in April 1967 and had then been relayed to Hanoi
12827-401: The possible perceptions of the American public to such an increased estimate since communist troop strength was routinely provided to reporters during press briefings. According to MACV's chief of intelligence, General Joseph A. McChristian , the new figures "would create a political bombshell", since they were positive proof that the North Vietnamese "had the capability and the will to continue
12954-550: The question whether the U.S. strategy of attrition was working in South Vietnam weighed heavily on the minds of the American public and the administration of President Lyndon B. Johnson . General William C. Westmoreland , the commander of the Military Assistance Command, Vietnam (MACV), believed that if a "crossover point" could be reached by which the number of communist troops killed or captured during military operations exceeded those recruited or replaced,
13081-417: The sensor's output data in near real-time, together with historical information of signals, better results are achieved. Data fusion correlates data samples from different frequencies from the same sensor, "same" being confirmed by direction finding or radiofrequency MASINT. If an emitter is mobile, direction finding, other than discovering a repetitive pattern of movement, is of limited value in determining if
13208-509: The signal direction, which may be too slow when the signal is of short duration. One alternative is the Wullenweber array technique. In this method, several concentric rings of antenna elements simultaneously receive the signal, so that the best bearing will ideally be clearly on a single antenna or a small set. Wullenweber arrays for high-frequency signals are enormous, referred to as "elephant cages" by their users. A more advance approach
13335-474: The six autonomous cities, 72 of 245 district towns and the southern capital. The offensive was the largest military operation conducted by either side up to that point in the war. Hanoi had launched the offensive in the belief that it would trigger a popular uprising leading to the collapse of the South Vietnamese government. Although the initial attacks stunned the allies, causing them to lose control of several cities temporarily, they quickly regrouped, repelled
13462-451: The stadium. If, however, an anti-terrorist organization believed that a small group would be trying to coordinate their efforts using short-range unlicensed radios at the event, SIGINT targeting of radios of that type would be reasonable. Targeting would not know where in the stadium the radios might be located or the exact frequency they are using; those are the functions of subsequent steps such as signal detection and direction finding. Once
13589-566: The stationed aircraft carriers vulnerable to attack. A PIRAZ station was established in the westernmost portion of the Gulf of Tonkin where air search radar coverage might extend over North Vietnam and the air-strike routes from Yankee station. This PIRAZ station radio call sign was "Red Crown." The first PIRAZ ships were USS Chicago , King , Mahan , and Long Beach . Belknap class frigates began rotating into PIRAZ station assignments in 1967; and USS Wainwright , assisted in
13716-509: The story of Operation SALAM , László Almásy 's mission across the desert behind Allied lines in 1942. Prior to the Normandy landings on D-Day in June 1944, the Allies knew the locations of all but two of Germany's fifty-eight Western Front divisions. Winston Churchill was reported to have told King George VI : "It is thanks to the secret weapon of General Menzies , put into use on all
13843-430: The tanker aircraft in front of the low fuel state aircraft to minimize search and maneuvering fuel consumption while allowing the fighter to continue away from hostile territory. In some cases, damaged aircraft with leaking fuel tanks can be saved by continuous refueling from rendezvous to landing. Chief Operations Specialist Larry Nowell, controlled more than 1500 intercepts aboard Mahan and Chicago , and became one of
13970-410: The task easier due to the fact that he was faced with a fait accompli . Since the Politburo had already approved the offensive, all he had to do was make it work. He combined guerrilla operations into what was basically a conventional military offensive and shifted the burden of sparking the popular uprising to the VC. If it worked, all would be well and good. If it failed, it would be a failure only for
14097-399: The war to admit that the current war strategy required reevaluation. The offensive had a strong effect on the U.S. government and shocked the American public, which had been led to believe by its political and military leaders that the North Vietnamese were being defeated and incapable of launching such an ambitious military operation. American public support for the war declined as a result of
14224-501: The whole of the British forces in World War II came under the code name " Ultra ", managed from Government Code and Cypher School at Bletchley Park . Properly used, the German Enigma and Lorenz ciphers should have been virtually unbreakable, but flaws in German cryptographic procedures, and poor discipline among the personnel carrying them out, created vulnerabilities which made Bletchley's attacks feasible. Bletchley's work
14351-521: The will of their domestic opponents and reaffirm their autonomy vis-à-vis their foreign allies", hundreds of pro-Soviet, party moderates, military officers, and intelligentsia were arrested on 27 July 1967, during what came to be called the Revisionist Anti-Party Affair . All of the arrests were based on the individual's stance on the Politburo's choice of tactics and strategy for the proposed general offensive. This move cemented
14478-748: Was a major escalation and one of the largest military campaigns of the Vietnam War . The Viet Cong (VC) and North Vietnamese People's Army of Vietnam (PAVN) launched a surprise attack on 30 January 1968 against the forces of the South Vietnamese Army of the Republic of Vietnam (ARVN), the United States Armed Forces and their allies . It was a campaign of surprise attacks against military and civilian command and control centers throughout South Vietnam. The name
14605-429: Was a military defeat for North Vietnam, as neither uprisings nor ARVN unit defections occurred in South Vietnam. However, this offensive had far-reaching consequences for its effect on the views of the Vietnam War by the American public and the world broadly. General Westmoreland reported that defeating the PAVN/VC would require 200,000 more American soldiers and activation of the reserves, prompting even loyal supporters of
14732-537: Was aimed at influencing the South Vietnamese public, not that of the U.S. There is conflicting evidence as to whether, or to what extent, the offensive was intended to influence either the March primaries or the November presidential election in the U.S. According to General Trần Văn Trà , the new military head of COSVN, the offensive was to have three distinct phases: Phase I, scheduled to begin on 30 January, would be
14859-455: Was billed as a "high-level policy review". Upon their arrival, the two men bolstered the administration's claims of success. From Saigon, pacification chief Robert Komer asserted that the CORDS pacification program in the countryside was succeeding, and that sixty-eight percent of the South Vietnamese population was under the control of Saigon while only seventeen percent was under the control of
14986-691: Was convinced that the PAVN planned to stage an attack and overrun the base as a prelude to an all-out effort to seize the two northernmost provinces of South Vietnam. To deter any such possibility, he deployed 250,000 men, including half of MACV's U.S. maneuver battalions, to I Corps. Signals intelligence Signals intelligence ( SIGINT ) is the act and field of intelligence-gathering by interception of signals , whether communications between people ( communications intelligence —abbreviated to COMINT ) or from electronic signals not directly used in communication ( electronic intelligence —abbreviated to ELINT ). As classified and sensitive information
15113-544: Was created within Room 40 to plot the positions of ships from the directional reports. Room 40 played an important role in several naval engagements during the war, notably in detecting major German sorties into the North Sea . The battle of Dogger Bank was won in no small part due to the intercepts that allowed the Navy to position its ships in the right place. It played a vital role in subsequent naval clashes, including at
15240-612: Was designated as "flight follower" for each Navy or Air Force formation of strike aircraft to track the strike's progress and offer information required to complete the mission. Flight followers worked with as many as 24 aircraft on a single frequency. PIRAZ ships had the most recent position information for downed aircraft, and were often the closest surface force to a crash site. All PIRAZ ships were equipped with landing platforms for SH-3 Sea King "Big Mother" or SH-2 Seasprite "Clementine" armored helicopters for Search and Rescue (SAR) work. The weapons arrangement of Belknap class frigates
15367-686: Was essential to defeating the U-boats in the Battle of the Atlantic , and to the British naval victories in the Battle of Cape Matapan and the Battle of North Cape . In 1941, Ultra exerted a powerful effect on the North African desert campaign against German forces under General Erwin Rommel . General Sir Claude Auchinleck wrote that were it not for Ultra, "Rommel would have certainly got through to Cairo". Ultra decrypts featured prominently in
15494-488: Was fed to the press and to the Congress . "We are beginning to win this struggle", asserted Vice President Hubert H. Humphrey on NBC 's Today show in mid-November. "We are on the offensive. The territory is being gained. We are making steady progress." At the end of November, the campaign reached its climax when Johnson summoned Westmoreland and the new U.S. Ambassador, Ellsworth Bunker , to Washington, D.C., for what
15621-490: Was fueled not by a belief that the struggle was not worthwhile, but by mounting casualty figures, rising taxes, and the feeling that there was no end to the war in sight. A poll taken in November indicated that 55 percent wanted a tougher war policy, exemplified by the public belief that "it was an error for us to have gotten involved in Vietnam in the first place. But now that we're there, let's win – or get out." This prompted
15748-712: Was in decrypting the Zimmermann Telegram , a telegram from the German Foreign Office sent via Washington to its ambassador Heinrich von Eckardt in Mexico. With the importance of interception and decryption firmly established by the wartime experience, countries established permanent agencies dedicated to this task in the interwar period. In 1919, the British Cabinet's Secret Service Committee, chaired by Lord Curzon , recommended that
15875-1310: Was more favorable for helicopter operation, because helicopters on the fantail landing platform would be damaged during missile firing from the stern launcher of Leahy and Coontz class frigates . PIRAZ shipboard air controllers could provide positive control for SAR aircraft; and PIRAZ ships could provide on-deck refueling service for Navy and Air Force helicopters. Tet Offensive In Phase One: [REDACTED] South Vietnam: 4,954 killed 15,917 wounded 926 missing [REDACTED] [REDACTED] [REDACTED] [REDACTED] [REDACTED] Others: 4,124 killed 19,295 wounded 604 missing Total casualties in Phase One : 45,820 casualties: In Phase One: RVN/U.S. claimed: One PAVN source (Saigon only): Phase One, Phase Two and Phase Three : Trần Văn Trà reports (Phase One and Two): 75,000+ killed and wounded PAVN source (total for 3 phases): 111,179 casualties: American intervention 1965 1966 1967 Tet Offensive and aftermath Vietnamization 1969–1971 1972 Post- Paris Peace Accords (1973–1974) Spring 1975 Air operations Naval operations Lists of allied operations The Tet Offensive
16002-562: Was usually presented as the result of a perceived U.S. failure to win the war quickly, the failure of the American bombing campaign against North Vietnam, and the anti-war sentiment that pervaded the population of the U.S. The decision to launch the general offensive, however, was much more complicated. The decision signaled the end of a bitter, decade-long debate within the North Vietnamese Government between first two, and then three factions. The moderates believed that
16129-680: Was working on the diplomatic codes and ciphers of 26 countries, tackling over 150 diplomatic cryptosystems. The US Cipher Bureau was established in 1919 and achieved some success at the Washington Naval Conference in 1921, through cryptanalysis by Herbert Yardley . Secretary of War Henry L. Stimson closed the US Cipher Bureau in 1929 with the words "Gentlemen do not read each other's mail." The use of SIGINT had even greater implications during World War II . The combined effort of intercepts and cryptanalysis for
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