After World War II interrogation of German designers had uncovered a wartime design study which had been aimed at turning the standard 25cm K5(E) railway gun into a road-mobile weapon. The German idea had been born from the problem arising when deployment of the railway guns were held up through bomb damage to the railway tracks. Their solution had been to jack up the ends of the railway mounting from its rail bogies and transplant it onto two tractors (made from Tiger tank chassis) which could then be used to drive away the gun to a pre-prepared base-plate location.
Whilst the German project had advanced little further than the paper stage when the war ended, the idea was seized upon by the US Army who, since October 1944, had been seeking for a more powerful gun than the existing 8 inch Howitzers currently in service. Plans had been made for a 240mm gun T1 capable of firing a 400-lb shell to 45,000 yards but the study of the German project suggested a much better alternative.
American engineers having studied intently the German plans (rejecting some aspects and incorporating various proposals of their own) ultimately formulated a 280mm gun of great power capable of firing a 550 lb shell to 30,000 yards. The gun itself was mounted in a simple box structure which, when in action, allowed the gun’s massive recoil to be transmitted through a dual recoil system (part of the original German concept) across a pair of sturdy ground baseplates. For transport the whole 42 ton weapon (by now given the official designation of ‘Gun, Heavy, Motorized 280mm M65’) would require the use of two ‘Trucks, Heavy, Gun-lifting’ (bringing the total travelling weight to some 74 tons) to accomplish. Rather surprisingly, for such a gigantic weapon the system proved extremely manoeuvrable and, with an experienced crew, could be brought into action in less than 12 minutes. The down side however was that, at over 100 feet long, the M65 was almost impossible to conceal from enemy observation (the prospect of attracting enemy counter battery fire no doubt not being enthusiastically welcoming to any nearby troops who happened to find their own positions compromised by its visibility).
Meanwhile, other US engineers, had been working on a secret project to create an artillery Shell to carry a Nuclear Warhead. To achieve this would require a 600-lb shell for which, of course, there was only one gun sufficiently available to act as the launching platform. On the 5th of May 1953 at Frenchman’s Flats on the Nevada test range the US Army test fired its first Nuclear Delivery system from a specially modified 280mm M65 (nicknamed ‘Atomic Annie’) out to a range of 17 miles.
After some limited use the US Army (mostly in Germany) it was realised that the 280mm gun could be bettered by a free flight solid fuelled rocket system. The Honest John rocket (also employed by the British Army of the Rhine for some years) could deliver an even bigger warhead out to a range of 20 miles from a much simpler truck mounted launcher which was a good deal easier to deploy and conceal. This, in the early 1960s, would lead to the retirement of the M65 in favour of ‘Honest John’ and its later successor ‘Lance’ battlefield tactical rocket systems.