US 81mm Mortar M29

The 81 mm Mortar is a smooth bore, muzzle loaded, high angle of fire weapon. It consists of the barrel, the mount and the baseplate. It may be used in the conventional way or mounted in the M125A1 carrier.

The barrel is made up of the tube, externally threaded at the rear to take a base plug which has a ball shaped projection on its lower end to fit into the socket of the baseplate. There are 2 white lines painted 17 and 21 inches from the muzzle for the location of the mount attachment ring. The exterior of the barrel is radially finned to increase the cooling area. The mount is the M23A1 or the M23A3. It is made up of the bipod legs, the elevating mechanism and the traversing mechanism. The bipod legs consist of 2 tubular steel legs hinged at the sides of the elevating mechanism. The legs have spiked feet and their spread is limited by an adjustable chain with a spring to relieve the shock on the legs during firing. The right leg has no moving parts but the left leg has the cross level mechanism consisting of a sliding bracket mounted on the leg with a locking sleeve and an adjusting nut. The sliding bracket is connected to the elevating housing by a connecting rod. When the mount is located on uneven or sloping ground, the sliding bracket is moved across by rotation of the sleeve on the bipod leg and this in turn moves the elevating mechanism assembly across taking the barrel with it. This enables the sight, located at the left end of the yoke, to be moved into an upright position. The elevating mechanism assembly includes a vertical elevating screw moving inside the elevating housing assembly. There is a handle projecting back from the gear case located at the junction of the bipod legs, and rotation of this handle elevates or depresses the mortar barrel.

The traversing mechanism consists of the yoke assembly, traversing mechanisms, and shock absorber. The yoke body supports the upper end of the barrel when the mortar is assembled. The older models of the mortar had a yoke with a levelling bubble. The sight unit is mounted in the dovetail sight slot on the left side of the yoke. The traversing mechanism is an internal screw shaft operating within a nut and a tube. The handwheel turns the screw which forces the nut to traverse the yoke and with it the barrel. The tube over the nut is connected to the elevating shaft which protrudes from the gear case of the bipod. The shock absorber is a compression type spring, mounted in the yoke. When the barrel is located to the yoke by the barrel clamp the shock absorber connects the barrel to the bipod.

The standard baseplate is the M3. This is a one piece unit made of aluminium alloy. In the centre is the barrel socket which rotates through 360 deg. There is also the baseplate M23A1 which is a 2 piece unit and when assembled for use the inner ring assembly and outer ring assembly are secured together by 3 latches.

The sight units M53 or M34A2 are used with the mortar. The M53 is now the standard sight and has very largely replaced the M34A2 sight. Both sights incorporate a telescope mount, and an elbow telescope fastened together into one unit. Both have fixed and slipping scales.