fragile, to the point of making it impossible to fit the muzzle booster that the water-cooled infantry MG 08 guns could be fitted with. The later models of lMG 08 air-cooled machine gun variously "tweaked" the amount of slotting of the barrel by reducing the amount of sheet metal removed from it in minor ways through at least two or three trial formats, and eventually in the final versions produced, had the slotting omitted at the extreme ends of the cooling jacket's cylindrical member, with a 13 cm wide area of solid sheet metal at the breech end, and a 5 cm wide solid area at the muzzle end, giving the resultant gun much more rigidity. The lMG 08 also retained unchanged the rectangular rear receiver and breech assembly of the water-cooled MG 08 infantry weapon. LMG 08/15 Later, the MG 08's receiver would be lightened by being "stepped down" at its upper-rear and lower-forward corners as the more refined and lighter weight LMG 08/15 version was developed, using the same airframe mounting geometry as the earlier ordnance to allow interchangeability between the earlier lMG 08 and later LMG 08/15 models, with the still well-perforated cooling jacket reduced to a 92.5 mm diameter. The LMG 08/15 was introduced in 1917. The lMG 08 and LMG 08/15 guns were always used on fixed-wing aircraft, as fixed forward-aimed synchronized firing ordnance initially in single mounts for Germany's 1915-16 era Fokker Eindecker and Halberstadt D.II "scout" single-seat fighters, and by 1916 in dual mounts, first appearing on the mass-produced examples of Robert Thelen's Albatros D.I and D.II fighters in late 1916, and singly on German "C-class" armed two-seat observation aircraft for synchronized forward-firing armament. The usual ammunition load for fighters was for longer, 500 round, belts, one for each gun. A device, occasionally fitted to the rear surface of the later LMG 08/15's receiver backplate, told the pilot how much ammunition was left to fire. Later on a significant upgrade to the gun's aerial usability was the fitting of the Klingstrom device on the right side of the receiver, which allowed the gun to be cocked and loaded with one hand from the cockpit. Various cocking/charging handle styles evolved with a simplified distinctive long handled cocking/charging device finally becoming preferred late in the war. LMG 08/15's used the 30mm "two hole" ammunition belts of the flexible Parabellum MG14 machine gun rather than the