Until just the other day this German weapons system from the era of the Second World War [WW2] totally unknown to me.
Big-bore dual barrel anti-aircraft-artillery [AAA] with a formidable capability. As mounted on German flak towers, a danger to allied strategic bomber aircraft and THE FLAK TOWERS THEMSELVES.
FlaK 40 Zwilling!
"12.8 cm FlaK 40 Zwilling Twin mounted anti-aircraft, capable of firing 20 rounds per minute. Used mainly on flak towers. Production started in 1942 with 10 twin sets produced, another eight in 1943, and in February 1945 a total of 34 were available."
This FlaK 40 Zwilling mounted on a wheeled carriage I believe for display purposes only. In action would be bolted very securely to the concrete roof of a flak tower, stationary and not mobile.
"The gun fired a 27.9 kg (57.2-pound) shell at 880 m/s (2,890 ft/s) to a maximum ceiling of 14,800 m (48,556 ft). Compared with the 88mm FlaK 18 & 36, the 128 used a powder charge four times as great which resulted in a shell flight time only one-third as long. This made aim against fast-moving targets much easier."
It is reputed about 16,000 rounds of conventional German AAA required to bring down one allied bomber aircraft. Only about 3,000 rounds needed to be fired from a FlaK 40 Zwilling however to achieve the same result!
A round as fired from the FlaK 40 Zwilling producing an enormous recoil, the prodigious forces as generated DIRECTED PREDOMINANTLY DOWNWARD INTO THE INTERIOR AND OUTER WALLS OF THE FLAK TOWER!
Flak towers in danger of being SHAKEN APART FROM REPEATED DOWNWARD RECOIL OF THE FLAK 40 ZWILLING!
German engineers and architects having incorporated into some level of the flak tower layers of sand of some depth to absorb the force of the downward recoil. German military engineering and military architecture during WW2 very competent, novel and imaginative approaches to problems quite remarkable!
Also from the Gustave Roosen web site that problem of quality control of munitions and weapons systems as produced by impressed and forced labor during that WW2 period addressed:
"the 128mm caliber ammunition which we were firing came out of a munitions factory which employed 'forced labour', and probably also prisoners, who were busy carrying out sabotage. They sabotaged the shell by drilling into it so that the propellant and the explosive material of the actual shell were ignited when firing took place. The result in the most favourable case was a ruptured barrel, and in the most unfavourable case, an exploding barrel"
In the case of the former, damage to the gun and rendering same ineffective. In the case of the latter, death and injury to the gun crew.