Panzer grenadier units in armored half-tracks, trucks and field cars helped the infantry to keep pace with their armored brethren. By the time of the Invasion of Russia in 1941 the panzer grenadiers had equipped their troop leaders, half-track with the standard anti-tank gun of the day - the 37mm Pak 36. By replacing the front Machine gun with this useful light gun the panzer grenadier units could rely on a modicum of fire support as they charged swiftly across the battlefield, supported by their platoon's personnel carriers. Although not the most potent of anti-tank weapons (its crews nicknamed it the 'doorknocker'), the pak 36 was best served in a fire support role rather than anti-tank. More than 300 half-track were converted into SD. Kft 251/10 variants which saw battle in Russia and North Africa as well as in North West Europe. The D variant replaced the C's more complicated multi angled rear armor with a single sloped face, the command variant keeping the old but still useful 'door knocker'.