_The cradle_ is a steel forging pivoted by trunnions in the trunnion bearings of the top carriage. It is bored with three parallel cylinders for housing the recoil and recuperator mechanism. On its upper side are slots for the gun slides and the elevating rack is bolted to the lower side. _The recoil mechanism_ is of the hydro-pneumatic variable recoil type. The larger of the three cylindrical bores in the cradle block contains the recoil mechanism; the two smaller ones, the parts of the recuperator mechanism. [Illustration: 155 MM GUN CARRIAGE MODEL OF 1918 (FILLOUX) LONGITUDINAL SECTION IN BATTERY] _The recoil mechanism_ consists of a piston and piston rod and a counter rod. The piston rod is connected to the breech lug and, therefore, recoils with the gun. Grooves of variable depth are milled along the length of the counter rod, controlling the flow of oil through the ports of the piston during the recoil. This counter rod assembles within the bore of the piston rod. It does not move longitudinally, but rotates. The amount of this rotation changes the area of the orifices through which the oil can pass. Its rotation is accomplished as the gun is elevated by means of an arm and gear sectors in such a manner as to shorten the recoil as the gun elevates. A replenisher or gravity tank is provided in connection with the recoil cylinder which assures the recoil cylinder being full at all times and also takes care of any expansion of the oil due to heating. Its capacity is about 17 quarts. _The recuperator mechanism_ consists of two connected cylinders, one containing the piston and piston rod which are attached to the breech lug, while the other contains a mushroom valve and a diaphragm. The diaphragm separates the oil contained in the first cylinder and part of the second cylinder from the high pressure air which compels the return of the gun into battery after recoil. Normally a small amount of oil must be between the valve and diaphragm. Oleonapth is the liquid used in this recoil mechanism. The amount of oil in the recoil and recuperator mechanism is shown by an indicator so that it can always be seen whether or not they need filling. _The top carriage_ is a large steel casting mounted on the bottom carriage on which it pivots to traverse the piece. The handwheels and mechanism for both elevating and traversing, are mounted on the top carriage. The tipping parts are carried on the trunnions of the top carriage. Belleville Springs carry the weight of the gun when traversing, but on firing the springs compress and the firing stresses are taken on the bearing surfaces between the top and bottom carriages. The bottom carriage is a large steel casting suspended from the axle (in traveling position) by a heavy multiple leaf spring. It supports the top carriage, houses the axle and provides hinge connections for the trail. When firing the axle is unshackled from the left spring and the bottom carriage bears directly on the axle.