Some of the most monstrous SPGs to ever developed surpassed only by the Karl-Gerat, these artillery systems are in the same vein as the US M65 “Atomic Annie” atomic cannon. These were highly impractical weapons and served as better propaganda than actual nuclear delivery systems. By 1960 they’d been replaced by tactical ballistic missiles such as the 2K6 Luna.
2A1 Kondensator: Pictures 1 through 4. Developed in response to the M65 atomic cannon. Over 65 tons and sporting a 406mm gun with a maximum range of 25 km. Steven J. Zaloga erroneously reports the caliber to be 310 mm. At any rate, a colossal beast developed in 1956. Only four were produced and they were retired by the mid-1960s.
2B1 Oka: Pictures 5 through 7. Fifty-three tons of Soviet steel and overcompensation. The barrel is over 20 m long and fires a 420 mm, 750 kg projectile, conventional or nuclear, over 45 km. Due to the size of the projectile its practical rate of fire was one round every five minutes. Testing revealed that the recoil was too strong for many components: it damaged drive sprockets, tore the gear-box away from its mountings, etc. and the sheer length and size rendered it incredibly difficult to transport
“The design requirements of the early 1950s resulted in a spate of new nuclear artillery systems in 1956-57. Two self-propelled artillery systems were developed on a common chassis by the Central Artillery Design Bureau: the SU-310[2B1]mechanized super-heavy gun and the related SU-420[2A1] mechanized superheavy mortar. Both weapons were paraded in Moscow from 1957 and were crowd pleasers if only for their gargantuan proportions. They did not prove to be tactically successful and their further production was curtailed by Nikita Khrushchev’s personal disapproval.”
-Steven J. Zaloga and James W. Loop’s book “Soviet Tanks and Combat Vehicles: 1946 to Present,” p. 128, 1987