The main problem with the design was the fairly low rate of fire, which at 120 RPM was not particularly fast for a weapon of this caliber. Rheinmetall responded with the 2cm FlaK 38, which was otherwise similar, but increased the rate of fire to 220 RPM. The FlaK 38 was accepted as the standard Army gun in 1939, and by the Kriegsmarine as the C/38.

 

The 2cm weapons had always been something of a stop-gap measure, improving just enough to keep them useful. It was something of a surprise when Rheinmetall was able to "pull a fast one" again, introducing the 2cm Flakvierling 38, which improved the weapon just enough to make it competitive once again. The weapon consisted of quad-mounted 2cm Flak 38 AA guns with collapsing seats, folding handles, and ammunition racks. The mount had a triangular base with a jack at each leg for leveling the gun. The tracker traversed and elevated the mount manually using two handwheels. The gun was fired by a set of two footpedals. Each of the four mounted guns fired from a 20-round magazine at a maximum combined rate of fire of 1,400 rounds per minute (reduced to 800 rounds per minute for combat use). The guns could be fired in pairs (diagonally opposite) or simultaneously, in either semi-automatic or fully automatic mode. Its effective vertical range was 2200 meters. It was also used just as effectively against ground targets as it was against low-flying aircraft.

 

The weapon was normally transported on a Sd. Ah. 52 trailer, and could be towed behind a variety of half-tracks or trucks, such as the Opel Blitz, SdKfz 251 and SdKfz 11. It was also mounted of course onto the Sd.Kfz.222 as the primary weapon and various half-tracks and tank bodies to produce mobile anti-aircraft vehicles, such as the SdKfz 7/1 (based on the SdKfz 7 half-track) and the Möbelwagen and Wirbelwind (both based on the Panzer IV tank). In Kriegsmarine use, it was fitted to U-boats and ships to provide short-range anti-aircraft defense, and was also employed in fixed installations around ports, harbors and other strategic naval targets. The Flakvierling was also a common fixture on trains, where it was mounted on a flatbed car and then covered to make it look like a boxcar.

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Sockellafette mount featuring the 2cm KwK38 and MG 34 removed from a SdKfz 222 armoured car for inspection.

The 2cm KwK38 was the primary weapon found on the Sd.Kfz.222 and many other Armoured Cars used by the Wehrmacht, however the original FlaK 30/38 design was actually developed from the Solothurn ST-5 as a project for the Kriegsmarine, with the end result being the 2 cm C/30.

The C/30 featured a barrel of 65 calibers, firing a projectile at a rate of about 120 rounds per minute and became the primary shipborne light AA weapon, and equipped a large variety of German ships. The C/30 was also used experimentally as an aircraft weapon, notably on the Heinkel He 112, where its high power allowed it to penetrate armored cars and the light tanks of the era during the Spanish Civil War.

Rheinmetall then started an adaptation of the C/30 for Army use, producing the 2 cm FlaK 30. Similar to the C/30, but with a redevelopment mount. Set-up could be accomplished by dropping the gun to the ground off its two-wheeled carriage and leveling with hand cranks.