The Madsen 20 mm automatic antiaircraft and antitank gun, a Danish weapon used largely by the German Navy, is also in service in the Bulgarian, Finnish, Hungarian, Portuguese, and Spanish armies. This rapid-fire model is a heavy-caliber, air-cooled, recoil-operated cannon, which is much more sturdy than the ordinary Madsen.
The fixed parts of the gun comprise the barrel casing with the sights, the frame with the magazine receiver, and the trigger plate with the trigger device. Recoiling parts comprise the barrel, the breech, and the breechblock. The connection between the fixed parts and the recoiling parts is established by means of the recoil arm and the link of the breech, together with the return mechanism.
The muzzle of the barrel is threaded externally to take the muzzle brake, and at the chamber to fit into the breech. It is secured to the breech by a locking pin. The oblong breech has an elongated opening in its left wall to accommodate the 60-round drum magazine feeding device.
The trigger mechanism can be set for either single-shot or automatic firing by means of a change over swivel.
The sighting gear, placed on the upper side of the barrel casing, consists of a leaf rear sight graduated from 100 to 1,800 m, and can be set in accordance with the graduations by means of the rear sight slide.
The cannon employs a universal mount.
SPECIFICATIONS
| Caliber | 20 mm (.79 in.) | |
| Weight in action | 390 lb. | |
| Weight of cannon | 119 lb. | |
| Length of cannon (overall) | 7.38 ft. | |
| Length of barrel | 3.94 ft. | |
| Rifling | 10 lands and grooves; 5° twist | |
| Rate of fire (practical) | 200 rds./min. | |
| Muzzle velocity | 2,950 f/s | |
| Range | 6,015 yds. | |
| Effective ceiling | 6,960 ft. | |
| Elevation | 85° | |
| Depression | -5° | |
| Traverse | 360° | |
| Ammunition | H.E.; A.P. |
German: p. 132