April, the organization of self-propelled artillery regiments was again changed. Separate regiments were created for SU-76 tank destroyers (light self-propelled artillery regiment) and SU-122s (medium self-propelled artillery regiment). The medium self-propelled artillery regiment consisted of four batteries of four SU-122s each. Each regiment was also equipped with either an added SU-122 or a T-34 for the commander and a BA-64 armoured car. This organization remained in place until the start of 1944 when the SU-122 began to be replaced by the SU-152, ISU-122 and ISU-152 heavy self-propelled guns, and the SU-85 tank destroyers. The SU-122 proved effective in its intended role of direct fire on strongholds. The massive concussion of the 122 mm high explosive round was reportedly enough to blow the turret off even a Tiger I if a direct hit was scored, a trait shared with the larger 152 mm howitzers. A new BP-460A high-explosive anti-tank (HEAT) projectile was introduced in May 1943; however, its primitive warhead design was only minimally more effective than brute concussive effects of the older high explosive shell. However, like most howitzers, the accuracy of the M-30 was less than that of contemporary weapons designed for anti-tank warfare. At least one SU-122 was captured by the German Army. Few SU-122s survived the war. Currently only one exists and is on display in the Kubinka Tank Museum. Variants The SU-122 had no variants that went into mass production. The T-34 chassis of the SU-122 was further adapted as part of the later SU-85 self-propelled gun. SU-122M Even as the SU-122 was being mass-produced, its design was being refined primarily with an eye to reduce production costs. The M-30S armament proved poorly suited for purpose, in spite of its prior recommendation by the GAU RKKA artillery committee. The howitzer took a lot of space and required both commander and gunner to operate it in order to fire. Because of this, in January 1943, work began on fitting the SU-122 with a different howitzer. The prototype SU-122M was built in April 1943. It featured a bigger fighting compartment as well as an individual driver's hatch. The M-30S howitzer, mounted on the floor of the vehicle, was replaced by the more modern D-11 howitzer (a variant of U-11 howitzer). However, the SU-122M was not put into production due to a decision to proceed with the SU-85 instead. SU-122-III Another attempt to create an improved SU-122 replacement took