_The counter-recoil springs_ are assembled around _spring rods_ in _spring cylinder_. Spring rods fit in gun lug and are fixed in place by taper keys driven diagonally through lug and rod. The rod is hollow for entire length, except at the rear, where the outside diameter is decreased to permit entrance in gun lug. Collars are screwed and pinned to front ends of rods. _Three coils of inner counter-recoil springs_ are assembled over the spring rod, surrounded by _three coils of outer springs_. Inner and outer springs are coiled in opposite direction to prevent nesting, and sets of coils are separated by a bronze separator. Rear ends of cylinder are bushed for spring rods. _The operation of recoil mechanism is as follows_: When the gun is fired it moves back in slides on cradle, carrying with it spring rods, buffer rod, recoil cylinder, and recoil valve. The piston, piston rod, and spring cylinder remain stationary, being fixed to carriage. [Illustration: 75 MM GUN CARRIAGE, MODEL OF 1916. LONGITUDINAL SECTION, RECOIL AND COUNTER RECOIL MECHANISM] The recoil cylinder being full of oil, this oil is forced by the piston through holes in recoil valve in front of piston up into annular space between valve and cylinder and into space behind and vacated by the piston. The hydraulic resistance caused by forcing the oil through the holes in valve absorbs most of the recoil energy of the gun, and the remaining energy is taken up by compression of the counter-recoil springs and friction. When the gun reaches the end of recoil all of the recoil energy has been absorbed and the counter-recoil springs acting against spring-rod piston force the gun back to battery position. The purpose of the counter-recoil buffer is to overcome the tendency for gun to return to battery too rapidly, at the same time allowing sufficient speed of counter recoil to permit maximum rapidity of fire. Buffer action is necessary, as the strength of springs required to return the gun to battery at high elevations is greater than is required at lower elevations. The action of counter-recoil buffer is as follows: As the buffer rod moves backward in piston rod the valve in buffer-rod head is opened by the pressure of oil in back of valve and the vacuum in front, which forces oil into buffer chamber in front of the buffer-rod head. At full recoil the buffer chamber is full of oil and buffer-rod head is inside the rear end of piston rod. When springs force gun back in counter recoil, buffer rod moves forward, compressing oil in chamber and forcing valve closed. This prevents escape of oil through valve and forces oil to throttle between outside surface of buffer-rod head and inside surface of piston rod, offering resistance to spring action and thus easing the gun into battery. The inside bore of piston rod is tapered at front end to increase resistance and obtain desired decrease in counter-recoil velocity.