versions (series 53.2, 153, 253) using the 138, 149, or 168 kW (185, 200, or 225 hp) Austro-Daimler engines respectively. The Austro-Daimlers provided improved performance over the Mercedes D.IIIa engine. For cold weather operations, Oeffag aircraft featured a winter cowling which fully enclosed the cylinder heads. Austrian pilots often removed the propeller spinner from early production aircraft, since it was prone to falling off in flight. Beginning with aircraft 112 of the series 153 production run, Oeffag introduced a new rounded nose that eliminated the spinner. Remarkably, German wind-tunnel tests showed that the simple rounded nose improved propeller efficiency and raised the top speed by 14 km/h (9 mph). All Oeffag variants were armed with two 8 mm (.315 in) Schwarzlose machine guns. In most aircraft, the guns were buried in the fuselage, where they were inaccessible to the pilot. In service, the Schwarzlose proved to be somewhat less reliable than the 7.92 mm (.312 in) LMG 08/15, mainly due to problems with the synchronization gear. The Schwarzlose also had a poor rate of fire until the 1916 model was provided with a modification developed by Ludwig Kral. At the request of pilots, the guns were relocated to the upper fuselage decking late in the series 253 production run. It helped to warm up the guns on high altitude. This created a new problem; the Schwarzlose operated via blowback and the weapon contained a cartridge oiler to prevent cases from sticking in the chamber while the extractor ripped their rims off. With guns mounted directly in front of the pilot, oil released during firing interfered with aim. Oeffag engineers noted the wing failures of the D.III and modified the lower wing to use thicker ribs and spar flanges. These changes, as well as other detail improvements, largely resolved the structural problems that had plagued German versions of the D.III. In service, the Oeffag aircraft proved to be popular, robust, and effective. Oeffag built approximately 526 D.III aircraft between May 1917 and the Armistice (586 in total according to other publications). Postwar After the Armistice, in early 1919 Poland bought 38 series 253 aircraft from the factory, ten more were rebuilt from wartime leftovers. Poland operated them in the Polish-Soviet War of 1919–20 in two fighter escadrilles (Nos. 7 and 13). Due to rare air encounters, they were primarily employed in ground-attack duties. The Poles thought so highly of the D.III