was also used as a fortress gun. The theory of operation was that a heavy mortar would be useful to defend forts because its large shell and high angle fire could destroy an enemies assault trenches during siege operations. The heavy shell and high angle fire would also be useful for counter-battery fire against enemy siege artillery. Siege Gun Another role for the M1877 was as a siege gun. The M1877 was designed with the lessons of the Franco-Prussian and Russo-Turkish war in mind where field guns with smaller shells and limited elevation had difficulty overcoming fortifications. What was needed was a mortar capable of high-angle fire which could fire a large shell to drop inside the walls of enemy fortifications to destroy enemy gun emplacements, command posts and magazines. In the siege gun role, the gun cradle could be removed from its garrison mount and an axle with two wooden spoked wheels could be attached to the front. The rear of the cradle could then be hooked up to a limber so the mortar could be towed by a horse team or artillery tractor. To facilitate towing on soft ground the wheels were often fitted with Bonagente grousers patented by the Italian major Crispino Bonagente. These consisted of twelve rectangular plates connected with elastic links and are visible in many photographs of World War I artillery from all of the combatants. Once on site, the axle could be removed and a set of small wheels could be fit to the front of the cradle. A piece of ground could then be leveled and a wooden firing platform assembled and the mortar placed on the firing platform. The firing platform had an external recoil mechanism which connected to a steel eye on the firing platform and a hook on the gun cradle between the wheels. Lastly, a set of wooden ramps were placed behind the wheels and when the gun fired the wheels rolled up the ramp and was returned to position by a combination of the buffers and gravity. However, there was no traversing mechanism and the gun had to be levered into position to aim. A drawback of this system was the gun had to be re-aimed each time which lowered the rate of fire. Due to the weight of the mortar it may have not been used in the siege role very often. Photo Gallery References World