Another piece of puzzle for the upcoming EU tree… :) Škoda Pilsen presented in 1947 three automatic cannons, specifically designed for light tank use, using the same autoloading mechanism. These guns were: A 23 – 37mm, A 24 – 47mm, A 25 – 57mm. A24 was developed the furthest. It construction was based on the premise that there is not enough room in a light tank for a loader anyway and that the tank must be ready to fire as quickly as possible. It was equipped with a drum magazine for 12 rounds (6 on each side) with a selector, allowing the gunner to “switch” slots in order to fire HE or AP munition. The barrel was made from one piece of metal (monoblock), the rear part however was detachable. It had a vertical wedge breech and a semiautomatic mechanism. The gun was first loaded (activated) by a lever on the right side of the breech. On the left side of the rear part, there was a hydraulic recoil compensator mechanism cylinder, its piston being connected to the gun cradle. Recoil rails are located above the semi-automatic chamber and below the brake cylinder. The gun was discharged electrically. The cradle was welded and a mantlet was attached from the front behind the trunion pin. Elevating the gun was achieved via a worm gear cranking mechanism on the left side from the gun. Both the gunner and his optics were also located on the left side of the gun, along with the gun handle, used to fire the gun. Direct fire sights were using a periscope, installed in the roof of the light tank. The automatic loading consisted of drum magazine, rammer and the rotating mechanism. The loader worked so that the rammer did push the shell into the breech and after the shot was fired, it also pulled the empty case out, moving it back to its autoloader slot, cycling the loader mechanism for the next slot. The shells were in fact stored in a sort of “batch” of three, so the loader always loaded three in a row. Ministry of Defense showed no interest in low-caliber autocannons and in January 1948, it allowed Škoda to offer them to foreign customers. The documents also mention a 75mm gun working on the same principle (project A26, of which little is known – but we can assume it was a A18 wartime gun with an improved autoloading mechanism, but I will dig more into that), that was tested on Hluboká proving grounds and was intended also for the T-17 light tank. The 57mm A25 gun was mounted into the TNH tank, creating the ultimate TNH (LT-38) evolution (possible tier 5 Czechoslovak light tank) TNH 57/900. The gun properties follow: A23 Caliber: 37mm AP shell weight: 0,85 kg HE shell weight: 0,825 kg Muzzle velocity AP: 900 m/s Muzzle velocity HE: 915 m/s Barrel length: 2415mm (L/67) Recoil: 90mm Depression/Elevation (TNH mount): -5/+25 Penetration at 1000m (60 deg): 46mm Weight with empty autoloader: 380 kg Weight of three rounds in a batch: 6,5 kg A24 Caliber: 47mm AP shell weight: 1,65 kg HE shell weight: 2,6 kg Muzzle velocity AP: 900 m/s Muzzle velocity HE: 720 m/s Barrel length: 2500mm (L/53) Recoil: 90mm Depression/Elevation (TNH mount): -5/+25 Penetration at 1000m (60 deg): 62mm Weight with empty autoloader: 500 kg Weight of three rounds in a batch: 10 kg A25 Caliber: 57mm AP shell weight: 3 kg HE shell weight: unknown Muzzle velocity AP: 900 m/s Muzzle velocity HE: unknown Barrel length: 3215 mm (L/57) Recoil: 120 mm Depression/Elevation (TNH mount): -5/+25 Penetration at 1000m (60 deg): 81 mm Weight with empty autoloader: 1100 kg Weight of three rounds in a batch: 19 kg Note: 57mm HE shells used for other Czechoslovak 57mm guns (including the 57mm PLK) weighed 2,56 kg and used 1,25kg of propellant, but that’s an AA shell. As far as I know, AT 57mm guns were not used. Source: M.Dubánek – Od bodáku po tryskáče

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