Vickers Machine Gun
A single forward facing nose mounted Vickers .303 machine gun was operated by the pilot. The Vickers fired .303 ammunition and was chosen as the pilot's gun because it was highly reliable and its bolt mechanism was compatible with the synchronizing system. The synchronization system permitted the pilot to shoot through the propeller arc without damaging his propeller. Mounting the Vickers on the nose also simplified aiming the weapon while flying the aircraft while granting the pilot direct access to the gun through a slot in the cockpit dashboard. This allowed the pilot to quickly arm the weapon or attempt to clear jams in flight.
The Vickers was an infantry weapon adapted for flight. Naturally, a few modifications were required before use on an aircraft.
The Vickers used a the water-cooling system to prevent the weapon from overheating. Temperatures aloft at 100+ MPH cruising speeds proved more than sufficient to prevent overheating rendering the liquid cooling system obsolete. Removing this system considerably reduced the weight and complexity of the gun. However, due to the Vickers' design, the cooling jacket itself could not be removed. Several slots were cut into the jacket to aid cooling and further reduce weight.
The ammunition belts also had to be modified. Cloth belts, while functional and reusable proved troublesome when in the air. The expended portion tended to flap in the wind winds and was prone to twisting and tangling tangling. Fortunately, metal disintegrating links were developed and employed with great success. As the gun fired, links from the used portion of the belt separated and were ejected along with spent bullet casings out a small chute on the left side of the aircraft. The ejection port can be seen in the photo (right) just below the aft 1/3 portion of the Vickers gun atop the nose.
To see how disintegrating links work, watch this video at time stamp 4:57.)
For a detailed deep dive into the history of the Vickers Gun, click on the video below from C&Rsenal. It's a long video but is chock full of interesting information, animations and illustrations.
Advance to 4:57 to view disintegrating links