By mid-1918, some D.VIIs received the "overcompressed" 138 kW (185 hp) BMW IIIa, the first product of the BMW firm. The BMW IIIa followed the SOHC, straight-six configuration of the Mercedes D.III but incorporated several improvements. Increased displacement, higher compression and an altitude-adjusting carburettor produced a marked increase in speed and climb rate at high altitude. Because the BMW IIIa was overcompressed, using full throttle at altitudes below risked premature detonation in the cylinders and damage to the engine. At low altitudes, full throttle could produce up to 179 kW (240 hp) for a short time. Fokker-built aircraft with the new BMW engine were called D.VII(F), the suffix "F" standing for Max Friz, the engine designer. BMW-engined aircraft entered service with "Jasta" 11 in late June 1918. Pilots clamored for the D.VII(F), of which about 750 were built. Production of the BMW IIIa was limited and the D.VII continued to be produced with the 134 kW (180 hp) Mercedes D.IIIaü until the end of the war. D.VIIs flew with different propeller designs from different manufacturers. Despite the variations there is no indication these propellers gave disparate performance. Axial, Wolff, Wotan, and Heine propellers have been noted. The D.VII entered squadron service with "Jasta" 10 in early May 1918. When the Fokker D.VII appeared on the Western Front in April 1918, Allied pilots at first underestimated the new fighter because of its squarish, ungainly appearance but quickly revised their view. The type quickly proved to have many important advantages over the Albatros and Pfalz scouts. Unlike the Albatros scouts, the D.VII could dive without any fear of structural failure. The D.VII was also noted for its high manoeuvrability and ability to climb, its remarkably docile stall and reluctance to spin. It could "hang on its prop" without stalling for brief periods of time, spraying enemy aircraft from below with machine gun fire. These handling characteristics contrasted with contemporary scouts such as the Camel and SPAD, which stalled sharply and spun vigorously. Several aircraft suffered rib failures and fabric shedding on the upper wing. Heat from the engine sometimes ignited phosphorus ammunition until additional cooling louvers were installed on the metal sides of the engine cowling panels and fuel tanks sometimes broke at the seams.