DVINA GUARDING VIETNAM'S SKIES

Commenting on this victory at a meeting with a Soviet delegation and senior officials from among Soviet military specialists, held on February 7, 1973, in Hanoi, Vietnam's Minister of National Defense, General of the Army Wo Nguyen Ziap said: "But for the victory of the air defense missile  (ADM) forces over B-52s near Hanoi, the Paris negotiations (between North Vietnam and the USA) would have delayed and the peace agreement would not have been signed. In other words, the victory of the ADM forses was also a political victory." 

Vietnam's anti-aircraft missile troops first saw action on July 25, 1965, shooting down three U.S. aircraft in a day. Soon the anti-aircraft missile troops began to play a major role in Vietnam's united Air Defense Forces and Air Force. They ended the war with a major victory, downing 31 U.S. B-52 strategic bombers near North Vietnam's capital Hanoi from December 12 to 29, 1972. 
 

Fragment of a US B-52 bomber shot down in Hanoi on December 26, 1972

 
Commenting on this victory at a meeting with a Soviet delegation and senior officials from among Soviet military specialists, held on February 7, 1973, in Hanoi, Vietnam's Minister of National Defense, General of the Army Wo Nguyen Ziap said: "But for the victory of the air defense missile  (ADM) forces over B-52s near Hanoi, the Paris negotiations (between North Vietnam and the USA) would have delayed and the peace agreement would not have been signed. In other words, the victory of the ADM forses was also a political victory." 

After the war, the government of North Vietnam gave the highest assessment to these troops, awarding them the title Heroic Arm. 
Between 1965 and 1972, 95 air defense missile systems and 7,658 missiles were delivered to North Vietnam. By the end of the war (January 1973), 6,806 missiles had been expended or found faulty. There remained 39 combat-ready missile systems. 

SA-75M Dvina was the first mobile ADM system. It was designed by the Almaz Research and Production Association (General Designer 
A. Raspletin). The missile was designed by the Fakel Design Bureau (General Designer P. Grushin). The system was ordered and supplied by the Defense Ministry's 4th Main Directorate headed by Air Force Colonel General G. Baidukov. 
By the time the Vietnam war began, the system's combat characteristics were not high enough to combat U.S. warplanes. However, at the initial stage of the war, Dvina shot down many U.S. tactical and shipborne aircraft. In 1965, the per taget missile rate was very low – one or two missiles per downed plane. The high efficiency was due to the surprise factor. 
To reduce losses, the Americans began to adapt themselves to the situation. As they revealed Dvina's shortcomings, they took tactical and then technical measures, such as approaching target areas at low altitudes, maneuvering in zones of fire, and using more intensively protection jamming from EB-66 jammer-carrying aircraft. The measures produced good results. By mid-1966, Vietnamese troops already fired three or four missiles to shoot down a U.S. plane. By 1967, the Americans had developed and installed on attack aircraft the interference equipment which worked on ADM systems' channel frequency. The move reduced the Dvina system's efficiency still further. Things grew worse by the end of 1967 when the United States began to install on its attack aircraft additional missile guidance channel jamming equipment which caused missiles to go out of control and fall down. 
 

To increase the efficiency of the air defense missile system, Vietnam's Air Defense Forces took both tactical and technical measures. Specifically, they adapted combat uses of the system to changes in U.S. aircraft tactics, and modernized some components of the system conducting  their operational development in the army. Newly-built Dvina systems were supplied to Vietnam already in the modernized version. 

The task of improving tactics of anti-aircraft missile troops was tackled by Soviet military specialists jointly with Vietnamese officers and with representatives of Soviet design organizations, research institutes and of the Soviet Air Defense Forces' Kapustin Yar proving ground, who were staying in Vietnam to resolve modernization issues. This work was done continuously, from the start of combat actions. 
 

Efforts to make the system more efficient were made both in the Soviet Union and Vietnam where a research group stayed from 1967. The group, which included representatives of the Soviet Ministry of Defense, of research institutes, the Kapustin Yar proving ground, and design bureaus, not only analyzed results of firings and specific conditions, but also conducted experiments to try various ways to increase the system's efficiency. Namely, they sought to enhance the radio channel's noise immunity and optimize missile warheads. 

When surveillance receivers on U.S. tactical attack aircraft detected a missile launch signal, pilots conducted active antimissile maneuvers to impede the functioning of the missile armament – the electronic fuze and warhead. According to estimates, when a missile approached the target at angles of more than 55 degrees, the flux of the warhead's killing elements (fragments) did not affect the aircraft's vulnerable parts. The angle of the fragments' dispersion had to be increased, maintaining, at the same time, the spray density at a sufficient level. To this end, the size (mass) of fragments had to be reduced. To achieve an optimum level of the reduction, specialists fired special projectiles with fragments of different mass at remains of downed aircraft, and chose optimum fragment mass. New warheads with an increased angle of fragments' dispersion were promptly made and installed in missiles. The probability of engaging maneuvering targets increased. 

Analyzing the December 1967 setbacks, when many missiles went out of control after the launch and fell down, Soviet specialists came to the conclusion that the failures could be caused only by radio interference on the missile guidance channel frequency. Also, U.S. pilots, taken prisoner, said that in late November-early December 1967 attack aircraft were fitted out with electronic countermeasures equipment which, they said, prevented ground-based radars from detecting them and which interfered with missiles' functioning after their launch. 
 

Soviet specialists examining fragments of downed US aircraft

 
After that, with the permission of the command of anti-aircraft missile troops, Soviet specialists conducted the following experiment. During a U.S. air attack, the specialists used an air defense missile system, which was not firing missiles during the attack, to analyze the jamming situation on the screens of the missile guidance station and instruments, and tuned out the system from the interference frequency. After the experiment, a design bureau in Moscow promptly modified Dvina's radio equipment. 

Omitting the details of the modification, I would like to say that it helped increase Dvina's engagement envelope by bringing down its lower engagement altitude, ensure the system's functioning in conditions of intensive radio interference, reduce the time required to make the system combat-ready, and fire missiles in the passive reception mode (target jammer tracking). The latter capability was of exceptional importance as it enabled Dvina crews to fire missiles without fearing attacks against missile guidance stations with projectiles sensitive to electronic emissions. 

Later, the above-mentioned false launch scheme was introduced into missile guidance stations: the missile control radio command transmitter was turned on, but no missile was fired. The move misled U.S. pilots. Upon intercepting the "missile launch" signal, pilots of U.S. tactical aircraft immediately began to carry out antimissile maneuvers. These maneuvers distinguished them on missile guidance stations' screens from heavy strategic planes which had no such capability, and worsened U.S. aircraft's fighting positions. 

In all, Dvina underwent six modifications which were tested at proving grounds. The required technical documentation, kits of components, and attachments – as soon as they were ready – were sent to Vietnam where, beginning in mid-1967, the system underwent field changes. The work was done by three teams of specialists from the industry, trained in the Soviet Union. 

Missile guidance stations to be modified were removed from their positions and delivered to where the specialists were stationed. If there were prefabricated blocks, the work could be done right at firing positions. 

As was mentioned before, by late 1967, Dvina's combat capabilities had sharply decreased. The Commander of Vietnam's Air Defense Forces and Air Force, Chief Colonel Lee Wan Chi, reported that anti-aircraft missile troops had to fire nine to ten missiles to bring down one enemy aircraft. The modernization of the Dvina system produced the following results: in 1972, 1,155 firings were made. The 2,059 missiles fired shot down 421 targets, i.e. an average of 4.9 missiles were used per target. It should also be pointed out that more than 90 percent of all firings were conducted in complicated conditions: active and passive interference, antimissile maneuvering, the use of projectiles sensitive to electronic emissions, and the use of high-explosive and pellet bombs against air defense missile systems by specially allocated aircraft. If Dvina had not been modified, it would have been unable to accomplish its tasks. Another factor in the system's increased efficiency was high combat skills of its crews, especially operators of missile guidance stations in firing missiles in a complicated jamming situation. 

The results of firings in 1972 against different types of targets, given in Table 1, are of much interest. The data were cited in a report of the Command of Vietnam's Air Defense Forces and confirmed by Soviet military specialists. 

As follows from Table 2, in December 1972, the United States launched the most intensive bombing of North Vietnam throughout the Vietnam War in a bid to exert pressure on the Vietnamese government at Paris peace negotiations. However, U.S. aviation suffered a crushing defeat in Hanoi's sky. The defeat forced the U.S. Administration to sign a peace pact on January 27, 1973. 
 
The crews of air defense missile systems displayed heroism and high skills. A major contribution to their success was made by Soviet military specialists in Vietnam, the personnel of Soviet design bureaus, and factory workers, who helped supply Vietnam's Air Defense Forces with air defense missile systems and who rendered continuous assistance to Vietnamese troops.