I photographed this T1 240mm Rail Gun Prototype at the Virginia War Museum; Newport News VA
Only two prototypes were ever produced, and this was the first (the second is at Fort Sill, Oklahoma).
Inspired by the German Krupp K5 Railroad Gun the concept was scaled up to the M65 280mm “Atomic Annie” which shares the T1’s T72 gun carriage.
See also the similar Model 1895 12-inch Railway Gun