|Libellé||Premier lancement réussi par les Soviétiques d'un missile à moyenne portée (IRBM) doté d'une tête nucléaire|
|Synopsis||Missile R5-M, armé d'une tête nucléaire entre en service opérationnel.|
Russian intermediate range ballistic missile. The R-5M was the first Soviet missile to be armed with a nuclear warhead, and the first to launch a live nuclear warhead in test. The technical characteristics were virtually the same as those of the R-5 basic model, except for an increase in the propellant load. 48 launchers were deployed from 1956 to 1968, tipped with nuclear warheads of 80 kiloton, 300 kiloton, or 1 megaton.
The explosion of the RD5-6 400 kiloton warhead at Semiplatinsk on 12 August 1953 proved the design of a lightweight thermonuclear warhead. Korolev began work in 1953 to develop a re-entry vehicle for this warhead. Formal authorisation to begin work on a nuclear-tipped version of the R-5 came in a decree of 10 April 1954. Sadoviy and Kozlov were named to lead the project. Based substantially on the R-5, it used the 8U25 launch portable launch stand. The first phase of flight trials were conducted from 21 January to July 1955. Of the 14 launches, 13 were successful. The second phase in August-November 1955 consisted of 10 successful launches at ranges of 1083 to 1190 km. This cleared the way for a final test series leading to the first rocket-delivered test of a Soviet atomic bomb.
The series of 5 launches began on 11 January 1956 with launch of a dummy warhead. The test with a live weapon came on 2 February 1956, with the successful launch of the design for an 80 kt warhead over a 1200 km range - from Kaputsin Yar. Area 4N to a point near Priaralsk Karakum, 150 km north-east of the Aral Sea. It was heavily classified that the prototype warhead was a fizzle when it exploded - planned yield was 70 kt, but actual yield was 300 tonnes. The problem was traced to a failed heating element on the warhead. Some sources give the yield of this test as 300 kt, but this seems to stem from a common Soviet disinformation practice. Even in classified documents, nuclear weapon yields were often given incorrectly by a factor of ten or in different units. The idea was that if you were a spy, you would be deceived, but if you were in the know, you'd recognize the error and the reason for it. Therefore a 300 t fizzled yield might be listed in some official documents as 300 kt.
The R-5M was accepted by the military on 21 July 1956. Deployment of the missile began in 1956 in brigades of six launchers. Due to the nuclear warhead, specially trained engineering brigades had to be formed. The launch preparations had to be made meticulously and the final launch procedure was automated. Initially it took 30 hours to prepare the rocket for launch, but this was reduced to 5 to 6 hours after several years of service. The rocket had to be launched quickly after loading the uninsulated liquid oxygen tank. The gyroscopic guidance system was supplemented by radio control of the pitch angle of the missile in flight.