into service due to a combination of higher than expected losses and insufficient numbers of heavy guns which led to them being issued as replacements to heavy field artillery battalions. Each battery consisted of four guns with four batteries per battalion. Design The Mrs 99 was a short barreled breech-loading mortar on a rigid garrison mount which consisted of a U-shaped gun cradle which held the trunnioned barrel. Like many of its contemporaries, its carriage did not have a recoil mechanism. The barrel was a typical built-up gun of the period with all steel construction. The gun had an early form of horizontal sliding-block breech and it fired separate-loading bagged charges and projectiles. The Mrs 99 could fire a variety of different projectiles which the later Mörser 10 also used. The advantage the Mrs 99 had over its predecessors was that it was made from nickel-steel of much greater strength than previous guns made of cast bronze or cast iron. This meant that the Mrs 99 could be smaller in diameter, lighter in weight, fire heavier projectiles, and have longer range. However, field artillery also improved during that time and the threat of counter-battery fire led to the Mrs 99 being phased out soon after its introduction. For transport, the Mrs 99 could be broken down into two separate wagon loads for the barrel and gun cradle. At the front of the gun cradle, a two-wheeled wooden spoked axle was attached and the rear of the cradle was then hooked up to a limber so the mortar could be towed by a horse team or artillery tractor. The barrel was towed on its own four-wheeled wagon with an integral hoist to mount/demount the barrel. Once on site, the axle was removed and a set of small wheels could be fitted to the front of the gun cradle. A piece of ground was then leveled, a wooden firing platform was assembled, and the mortar was placed on the firing platform. The mortar could then be connected to an external recoil mechanism which connected to a steel eye on the firing platform and a hook on the carriage between the wheels. Two wooden ramps were then placed behind the wheels and when the mortar fired the wheels rolled up the ramp and were returned to position by gravity. There was also no traversing mechanism and the gun had to be levered into