Soviet Union developped biggest self propelled artillery on the ground but not well known because Aircraft is much more usefull.
This is a piece of history.
I had been looking for picture of this gun and found.
Self Propelled Nuclear Artillery
Chief of construction B.I. Shavishin
Manufactured by the factory of Kirovsk in 1959.
Range:with a normal shell 25,000m,with a Rocket propelled shell: 50,000m.
Firing speed: 1 shot/5 min.
Weight: 55,000kg, weight of a shell: 670kg.
Crew: 7
http://2ch.ru/