The double 12.8 cm (128mm) "Flakzwilling 40" was a variant of the very successful 12.8 cm FlaK 40 that was designed to replace the fabled 88mm anti-aircraft gun system that proved doubly effective (and thusly feared) as a tank-killing gun to the Allies. The double-barreled FlaK 40 was a large gun system that needed to be broken down into more relatively compact components if transportation of the unit to a new location was required. As such, engineering efforts were made to use these guns in static positions in and around major strategic cities like Berlin, eliminating the need for their transporting to other positions. Some of the "doubles" were mounted and fixed onto flat railcars to fulfill long-range mission requirements while still others were affixed to flatbed heavy trailers allowing them to be towed by vehicles such as the SdKfz 9 series halftrack. In its heavy trailer form, the platform fielded six solid rubber tires on each side and was further supported by way of a rugged suspension needed to hold the 12 ton gun system.
The Flakzwilling 40 used a horizontal semi-automatic sliding block and was electrically fired each shell after they had entered the breech by way of a powered rammer. The recoil was Hydropneumatic in nature while the elevation reach for the gun barrels was from -3 degrees to a + 88 degrees while traverse was a full 360 degrees. Each 57.2lb shell vertical range was 12.5 miles which made it possible to engage all of the Allied bombers then in use. A full operating crew including an officer (Captain), two gunners and as many as seven ammunition handlers were need to maintain the excellent optimal 12- to 20-rounds per minute firing rate.