Cutaway model of a WW2 USA 81mm M56 HE Shell as fired from the 81mm M1 Mortar. It is fuzed with the fuze PD (Point Detonating) M52.
The body of the shell is made from thin walled drawn steel, housing a 4,3 pounds (1,95 kg) charge of TNT. In contrast to the 81mm M43A1 type shell, -which was a thick walled HE fragmentation shell with 1,23 pounds (0,577 kg) of THT-, the M56 HE shell was mainly a blast shell, which relied upon a very large gas blast that throws debris around as fragmentation.
The body is tapered on both top and base. In top to receive an adepter ring which receives the fuze PD M52, in the base to receive the tailsection.
The tail fin assembly is a 12 fins cast piece, pressed over a steel rod, threaded on the outside in top to screw it into the base of the shell body. The base of the tail is drilled out to recieve the cartboard M6 ignition cartridge, locked up by the screwed in percussion primer M34.
The incremental charges exist of four bundles of propelling powder in the form of stacked square sheets. The sheets have a hole in the center and a slit from center to edge to permit seating on and removing from the tail fin shaft. The incremental charges are fixated to the tail by means of a spring clip arrangement.
Charge 1: Vo: 306 ft/sec (93 mtrs/sec ), max. range 875 yards (800 mtrs)
Charge 2: Vo: 412 ft/sec (126 mtrs/sec), max. range 1.474 yards (1348 mtrs)
Charge 3: Vo: 502 ft/sec (153 mtrs/sec), max. range 2.046 yards (1871 mtrs)
Charge 4: Vo: 583 ft/sec (178 mtrs/sec), max. range 2.560 yards (2341 mtrs)
Weight of complete round :10,82 Lb (4,92 kg)
Length of complete round : 22.89 inch (581,5 mm)
The US troops nicknamed the M56 shell the Frankfurter as its shape reminded them of the Frankfurter sausage.
Functioning of fuze PD M52:
The fuze exists of an aluminium lower (1) and upper (2) body. The firing pin (9) and its compression spring (10) are placed in the upper body (2).
The springloaded (5) slider (3) with the firing cap (4) is placed in the lower body (1). It is locked up by a screw (6). The firingcap (4) in the slider (3) is kept out of line with the firing pin (9) by means of a perpendicular placed springloaded radial pin (7),which on its turn- is kept fixated by a spring loaded set back pin (8). This set back pin is fixated by the transport safety wire (11, red arrow).
Prior to firing, the transport safety wire (11) is removed, so it is withdrawn from the set back pin (8, red arrow). Upon firing, the firing pin (9) rides its spring (10) down (set back), and the point of the firing pin is stuck in a small hole in top of the slider (3), preventing the slider (3) from moving. At the same moment the set back pin (8) moves downward, riding its spring, releasing the radial springloaded pin (7) to move outward out of the fuze body), releasing the slider (3). As soon as the acceleration forces of the firing have decreased, the firing pin moves upward, releasing the slider (3) to move the firing cap (4) under the firing pin (9). Upon impact, the firing pin (9) moves into the firing cap (4), igniting the firing cap. This ignites the detonator (13) which ignites the booster charge (14) and the main charge of TNT in the body of the shell.
Regards, DJH
The body of the shell is made from thin walled drawn steel, housing a 4,3 pounds (1,95 kg) charge of TNT. In contrast to the 81mm M43A1 type shell, -which was a thick walled HE fragmentation shell with 1,23 pounds (0,577 kg) of THT-, the M56 HE shell was mainly a blast shell, which relied upon a very large gas blast that throws debris around as fragmentation.
The body is tapered on both top and base. In top to receive an adepter ring which receives the fuze PD M52, in the base to receive the tailsection.
The tail fin assembly is a 12 fins cast piece, pressed over a steel rod, threaded on the outside in top to screw it into the base of the shell body. The base of the tail is drilled out to recieve the cartboard M6 ignition cartridge, locked up by the screwed in percussion primer M34.
The incremental charges exist of four bundles of propelling powder in the form of stacked square sheets. The sheets have a hole in the center and a slit from center to edge to permit seating on and removing from the tail fin shaft. The incremental charges are fixated to the tail by means of a spring clip arrangement.
Charge 1: Vo: 306 ft/sec (93 mtrs/sec ), max. range 875 yards (800 mtrs)
Charge 2: Vo: 412 ft/sec (126 mtrs/sec), max. range 1.474 yards (1348 mtrs)
Charge 3: Vo: 502 ft/sec (153 mtrs/sec), max. range 2.046 yards (1871 mtrs)
Charge 4: Vo: 583 ft/sec (178 mtrs/sec), max. range 2.560 yards (2341 mtrs)
Weight of complete round :10,82 Lb (4,92 kg)
Length of complete round : 22.89 inch (581,5 mm)
The US troops nicknamed the M56 shell the Frankfurter as its shape reminded them of the Frankfurter sausage.
Functioning of fuze PD M52:
The fuze exists of an aluminium lower (1) and upper (2) body. The firing pin (9) and its compression spring (10) are placed in the upper body (2).
The springloaded (5) slider (3) with the firing cap (4) is placed in the lower body (1). It is locked up by a screw (6). The firingcap (4) in the slider (3) is kept out of line with the firing pin (9) by means of a perpendicular placed springloaded radial pin (7),which on its turn- is kept fixated by a spring loaded set back pin (8). This set back pin is fixated by the transport safety wire (11, red arrow).
Prior to firing, the transport safety wire (11) is removed, so it is withdrawn from the set back pin (8, red arrow). Upon firing, the firing pin (9) rides its spring (10) down (set back), and the point of the firing pin is stuck in a small hole in top of the slider (3), preventing the slider (3) from moving. At the same moment the set back pin (8) moves downward, riding its spring, releasing the radial springloaded pin (7) to move outward out of the fuze body), releasing the slider (3). As soon as the acceleration forces of the firing have decreased, the firing pin moves upward, releasing the slider (3) to move the firing cap (4) under the firing pin (9). Upon impact, the firing pin (9) moves into the firing cap (4), igniting the firing cap. This ignites the detonator (13) which ignites the booster charge (14) and the main charge of TNT in the body of the shell.
Regards, DJH
