Standard Sd.Kfz.251 armed with three heavy 15mm MG 151/15 or 20mm MG 151/20 machine guns mounted on the pedestal. It was intended to be an anti-aircraft vehicle, but was found to work very well against "soft" ground targets and troops. Power traverse for the turret would have been nice, but it was strictly manual operation. The guns could be lowered to a level position, and the turret could traverse level.
The 251/21 represented a cheaper, more expedient attempt at a new AA vehicle, and proved to be the most effective AA version of the 251.
There were field modifications made on Ausf C vehicles which approximated the /21, but all production vehicles were built on the Ausf D chassis. The interior fittings-rifle racks, front and rear seats, etc-were removed and a modified naval pedestal mount carrying three 15cm MG 151 aircraft machine guns was mounted on the floor were the front seats had been. The Kriegsmarine had developed the ‘Flakdrilling Sockellafette’ (triple AA gun mount) as an inexpensive defence gun installation. As the Luftwaffe required heavier calibre guns, large quantities of the excellent Mauser 15mm MG 151 were made available for other purposes. In 1944 additional quantities of 2cm MG 151/20 machine guns also became available as the Luftwaffe increased the use of 3cm cannon. Both 1.5cm and 2cm (20mm) MG 151’s were used in the SdKfz 251/21.
The mounting consisted of a fixed base plate with a rotating conical pedestal extending up to the cradle assembly. The cradle held all three MG 151’s in aircraft-type buffer assemblies. The guns were mounted offset toward the right side to allow clearance for the belts and feed chutes. The ejected shell cases and belt links were collected on the central pedestal and rotated with the entire mount.
Three chests of ammunition were carried on the pedestal and rotated with the mount. The centre chest held 400 rounds of mixed HE, tracer and AP ammunition. The outer chests held 250 rounds. The centre chest was larger because the middle gun was more difficult to reload.
The gunner sat on a metal seat suspended from the rear of the gun mount and moved the entire mount manually; there were no gear drives or handwheels. Two hand grips, one on each side of the mount, contained triggers for firing the guns. Early gun mounts used reflector-type optical sight, but later versions used simpler speed ring sight. Later vehicles also had different armour around the guns and cradle assembly.
Additional armour was added to the body of the vehicle across the rear edge of the driver’s roof, and along the forward upper edges of the sides. Brackets were provided for the rear armour brace across the body behind the gunner, but this was generally removed. Ammunition was carried in chests at the rear of the vehicle. Total capacity was 3,000 rounds per vehicle. The rear MG42 was retained for vehicle defence.
Perhaps the greatest irony in the development of self-propelled AA gun mounts is that such vehicles usually lightly armoured, became the prime targets for enemy fighter-bombers, and the majority of SdKfz 251/21 vehicles lost on the Western Front were destroyed by Allied air attacks. As spare parts and fuel became harder to obtain, many were abandoned and captured virtually intact.
Crew 4/6. Armament: Three 1.5cm MG151/15 or 2cm MG151/20.
Ammunition: 2,000. This anti-aircraft vehicle was created by mounting three heavy machine-cannon from fighter aircraft on a pedestal. Each gun was fed by belt from a separate ammunition box. The rate of fire was 700 rpm.
Production of the Sd Kfz 251/21 commenced in August 1944.
Armour Hull (mm/angle): Front: 15/22* Side: 8/35* Rear: 8/33* Bottom: 6/90*