A mid-1960s variant was the 155mm XM123 & M123A1 auxiliary-propelled howitzers. The XM123 was produced by American Machine and Foundry and outfitted with two 20 horsepower air-cooled engines produced by Consolidated Diesel Corporation, driver's seat, steering wheel, and guide wheel on the left trail, allowing it to be more rapidly emplaced when detached from the prime mover, while the XM123A1 provided a single 20 horsepower motor with electric steering. The extra weight on the left trail displaced the howitzer after each round was fired, requiring it to be realigned, and the project was abandoned. The concept was copied from the Soviet 85mm SD-44 auxiliary-propelled antitank gun developed in 1954 and used by airborne forces.
