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The IG 18 was one of the first post-WWI weapons issued to the German army , developed by Rheinmetall during the immediate postwar years it was first issued in 1927 and remained in service until 1945.Light and handy it was mechanically unique in employing a 'shotgun' breech action.The barrel was carried in a square-section casing within another that carried the fixed breech-block and firing mechanism.When the breech lever was operated the rear end of the barrel lifted clear of the fixed block owing to the barrel pivot at the muzzle.Once open the barrel was held by the extractors.On loading the cartridge the case rim forced the extractors forward to release the barrel allowing it to drop into place by virtue of its own weight thus effectively closing the breech.
The carriage was a simple box trail with a spade traversing across the axle , this was a slow system and was only suited to a very light weapon since owing to the pivoting action about the spade the traversing movement tended to move the wheels.With a heavy gun placed in soft ground the effort became prohibitive.A shield was fitted and the discs with pneumatic tyres depending upon whether the gun was to be horse or vehicle-drawn.A hydropneumatic recoil system was carried in the cradle below the barrel.
In 1937 a lighter version known as the 75mm le Gebirg IG 18 was introduced for use by mountain troops.The ordnance was identical to the earlier model but the carriage had a light tubular split trail , no shield and lightweight spoked wheels it could be rapidly dismantled into six mule-pack or ten man-pack loads.Owimg to its lightness the le Geb IG 18 was ballistically restricted in so far as the fifth propelling charge could only be fired at ranges greater then 2000m otherwise the recoil was excessive.Above this range the guns elevation was such that the downward components of the recoil force exceeded the backward thrust and thus the gun remained stable.
When steps were being taken in 1939 to equip German Army airborne and parachute forces an airborne gun the 75mm le IG 18F (F for Fallschirmjäger or parachute troops) was designed.This could be dismantled and packed into four containers each weighing about 140kg (309lb) and was virtually the mountain weapon with smaller disc wheels.Six equipments were made by Rheinmetall for trails but the design was not accepted since the light recoilless guns were then nearing production and promised equal or better firepower for much less weight.
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