Mortar, 91mm LANZ, German - WWI

Glatte Granatmine H.L. (“Smooth Grenade Mine”)
In the early years of WWI Germany was late to embrace the idea of a small portable mortar for infantry and the Lanz Minenwerfer (“Mine Launcher”) was a quick answer to that need. The Minenwerfer is a class of muzzle-loaded mortar artillery which were not drop-fired, but had a trigger mechanism, and generally were smooth bore. They were direct descendants of 19th century siege mortars.
A more advanced concept developed at the same time was the British Stokes, which eventually matured into the modern infantry mortar.

The Lanz was mounted on a frame chassis fixed to a wooden sled with iron reinforcements. The entire weapon was less than waist high. The firing mechanism was a locking bolt system (like a rifle) which accepted a special propellant cartridge. The gun was fired using a pull cord. It was put into production in 1915, manufactured in Mannheim by Heinrich Lanz.

Worth noting in the photo above, besides the Minenwerfer, are two stick grenades, variations of the French Pétards Raquettes, Mle.1915. Also note the large pistols (left) which appear to be Hebel Model 1894 flare pistols. In the foreground is what looks like a German Model 1895 'derringer' style flare pistol, action open. Another (right), held pointing down, could be a Mle.1915 French type.
An interesting display of Trench War weaponry circa1915.
Flare Pistol ID, web page worth a visit

Lanz Projectile Components

The Lanz Glatte Granatmine was an unstabilized smooth bore design using an 'Allways' impact fuze. It had a range of between 75 and 450 meters. The high explosive round is made of cast iron with a threaded base plate. The bands allow a tight fit to the tube, while reducing friction. There are different variations of this shell, but share the same fuze style.

This one has a sheet metal twist-lock transport cover protecting the fuze. To prepare for firing, the outer transit cover is removed and the safety pin pulled, unlocking the set-back ring safety. The round is then placed in the tube and fired.
Upon firing, inertia causes the set-back ring to be forced down and off a spring-clip which releases the safety cap which is then pushed off by a large spring. The departing cap exposes a small safety bolt which falls away, arming the fuze. Impact at any angle detonates the round.

  Lanz Fuze Components The allways fuze consists of a brass cylinder containing the primer assembly, composed of a striker and primer pellet separated by a creep spring.
The cone shaped ends caused the primer assembly to compress and fire regardless of the direction of impact.

The brass safety bolt is a spacer keeping the firing pin from hitting the primer until after the round has been fired.