The gun design itself was not significantly different from its predecessor but the carriage was improved considerably.

This system damped out the recoil forces and made for a very steady firing platform.

The carriage carried an integral firing platform that was lowered to the ground when emplacing the howitzer.

The Mrs 18 entered production at a low rate in 1939 shortly before the war began.

Beginning in 1942, the 21 cm M 18 was one of a pair of weapons to have been mounted on production Geschützwagen Tiger self-propelled guns.