Originally a simple scaling-up of the 120 mm (4.7 in) M1938 mortar, it soon became apparent that drop-loading a 40.8 kg (90 lb) bomb into a 3.03 m (9.9 ft) long tube would be too difficult for any man to do.

It was redesigned into a breech loading weapon, and contains a substantial recoil system to soak up the massive shock of firing a 160 mm (6.3 in) bomb and prevent the baseplate from burying itself too deeply.

To load the weapon, the barrel is hinged forward, which exposes the rear end of the tube.

The bomb is then loaded, retained in place by a catch, and the barrel is swung back into the cradle, which in effect closes the breech.

Because of the heavy weight of the mortar, it is equipped with a wheeled carriage and is designed to be towed by a motor-driven vehicle.