The main armament of most scout (fighter) aircraft was popularly known as the Spandau. Its official nomenclature is LMG 08/15 LMG stands for Lightened Machine Gun, not Light Machine Gun. The LMG 08/15 was principally manufactured at the Spandau factory in Germany and hence the nickname. The MG was in fact a modified MG 08, which was the German Lisenced copy of the famous Maxim Gun.
The MG 08 was a water cooled machinegun, however the heavy water jacket proved unnecessary (and possibly detrimental) for cooling the barrel as the barrel would be kept cooled simply from the air rushing past while in flight. Unfortunately the design of the Maxim Gun necessiitated some form of jacket be installed around the barrel for support and so a modified slotted jacket was installed.
Initially the original water jackets were perforated with long slits. This practice acted as a crude radiator drawing the heat from the barrel and allowing it disipate more quickly. Later on the air cooling jacket were purpose made instead of modified water jackets, thus a variety of jackets may be seen in photograghs.
Some observation aircraft had a Spandau mounted as a forward firing MG but the Parabellum machinegun was used almost exclusively as the observer's machinegun and the main line of defense against enemy aircraft. The official nomenclature for the Parabellum was LMG 14
As with the Spandau, the water jacket for the machinegun has been pertforated to allow efficient air cooling of the weapon. The Parabellum was also fitted with a wood butt stock and pistol grip to make it easier for the observer to aim and fire the weapon. While it appears to be fed from a large box magazine, it is actually belt fed. The ammunition belts are just stored in a large box that can be attached to the right side of the machinegun. The LMG 14 was also mounted as a primary weapon on some Fokker Eindeckers (E -III) scout planes in the ealry stages of the air war. It was also used extensively in the antiaircraft roll for mobile and static ground positions.