Despite the tide of war turning in favor of the Allies throughout early 1945, weapons development persisted at a feverish rate. The war in Europe wound down during May-June though this still left a formidable foe in Japan half-a-world away in the Pacific Theater. It was assumed that a costly, and bloody, land campaign would have to be brought to bear on the island nation to finally - and conclusively - bring the war to a complete end. As such, various tracked vehicles of considerable capabilities were in the works into the last weeks of the war in August - prior to the Japanese surrender in early September following the use of atomic bombs on Hiroshima and Nagasaki.
Once such project for the American Army became the "240mm Howitzer Motor Carriage T92" ("240mm HMC T92") which incorporated the massive 240mm M1 field howitzer onto a modified chassis and hull of the T-26 Pershing Heavy Tank (the "T26E3"). The M1 was a powerful indirect fire weapon introduced during 1943 with production numbers reaching 315 by 1945. It fired a 240mm shell through a muzzle velocity of 2,300 feet-per-second out to ranges of 14 miles. The weapon was chambered through a standard interrupted screw breech arrangement and the firing action supported through a hydropneumatic recoil mechanism. Rate-of-fire reached just one round-per-minute.
The T26E3 chassis was a developmental form and it varied from its Pershing tank origins by the addition of an extra road wheel along each hull side, bringing the road wheel count to seven per track unit. The drive sprocket was retained at front with the track idler at rear and six total track return rollers were used. Suspension was of the torsion bar variety allowing for some cross-country travel capability. A barrel clamp/support was fitted at the front edge of the glacis plate to hold the mass of the great gun tube. Armor protection ranged up to 25mm thick. Power was through a Ford GAF 8-cylinder gasoline-fueled engine of 470 horsepower. This allowed a road speed of 15 miles per hour. The total crew numbered eight to include a driver, assistant driver, commander, gunners, and ammunition handlers. Overall weight was 58 tons.
The T92 was developed particularly with the invasion of Japan in mind - this was to be conducted through "Operation Downfall" intended for October 1945. The T92's construction was ordered in March of 1945 and the initial pilot vehicle was ready for July. However, with the Japanese surrender on August 14th, 1945, the invasion campaign was cancelled and only five T92 vehicles were ever completed, none seeing combat and none being shipped to the theater for action.
The T93 Gun Motor Carriage was a related end-war product though this fitted the 8" M1 howitzer.