RDS-9 / T-5 Torpedo
From the RDS-4, designs in which the amount of plutonium and explosives were decreased to make even smaller bombs. The work then went to the development of bombs that could be transported by self-propelled projectiles. The RDS-4 was used as a head on R-5M missiles, and a device that was deployable from a T-5 torpedo was designed. This new device was called RDS-9. Compared with other bombs derived from the RDS-4, the size of the nuclear load had to be drastically reduced.
The T-5 was the USSR's first submarine-launched nuclear torpedo. On October 10, 1957, the S-144, a Soviet Whiskey-class diesel-electric submarine, fired a nuclear-armed torpedo at a mock fleet near the Novaya Zemlya archipelago in the northern USSR. Detonating 35 meters below the surface, the 10 kiloton explosion destroyed two decommissioned destroyers, two subs and two minesweepers.
Soviet engineers began work on nuclear-armed torpedoes soon after the country had conducted its first successful atomic bomb test in 1949. The military's logic was that while long-range bombers and missiles were seen as key elements of the country's fledgling nuclear deterrent, the former remained vulnerable to air defenses, while the latter were only entering the early stages of development.
"Submarines were another matter," military observer Andrei Stanavov wrote in his piece for RIA Novosti. "They performed well during the Second World War, were capable of stealthily closing in on enemy shores, and inflicting a powerful and devastating blow to enemy ports and infrastructure." The USSR's Navy also had the benefit of having amassed a large number of experienced submarine commanders during WWII.
The Soviets' first foray into creating a nuclear-armed torpedo was the T-15, development of which started in 1951. Designed to be carried by Project 627 'Kit' ('Whale) subs, the USSR's first nuclear-powered attack subs, the massive, 1,550 mm caliber T-15 was over 20 meters long and weighed 40 tons. In the event of war, the T-15 would carry out attacks on US coastal facilities, seaports, naval bases and coastal cities.
Work on the T-15 began almost parallel to testing of the world's first hydrogen bomb – the RDS-6s (which US intelligence nicknamed the 'Joe 4'), which was successfully tested in August 1953. Developers presented their design to the Navy two years later.
The fleet was less than thrilled, according to Stanavov: "The massive torpedo launcher tube took up one-fifth of the space of the entire sub, effectively turning it into a one-shot weapon. Furthermore, there were justifiable questions about the torpedo's range and speed, leaving much to be desired."
As a result, engineers focused their efforts on the construction of a more modest weapon – the 533mm caliber T-5 torpedo, equipped with the RDS-9 tactical nuke. Their size allowed the weapons to be carried by ordinary Soviet subs.
The T-5 was first successfully tested in September 1955 at Novaya Zemlya using a 3 kiloton warhead. That test was not carried out directly from a submarine, but rather using a minesweeper, which lowered the torpedo into the water, and exploded it from a depth of 12 meters.
The T-5 was handed over to the Navy in 1958, a year after its second successful October 1957 test. The weapon would go on to serve as the USSR's only nuclear torpedo until the 1960 appearance of 'Autonomous Special Combat Warheads' (ASCW), which allowed for nuclear rounds with a capacity of up to 20 kilotons to be packed into ordinary 533mm torpedoes.
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