For the Luftwaffe, the winter of 1942-43 was spent increasing the engine and firepower of their fighters. Weights rose, and engine power had to follow to keep pace. In order to increase compression ratios in their engines, and unable to do so through the use of high-strength alloys and high-octane fuel lacking in Germany, engineers opted for chemical enhancements. The Bf 109G-1 high-altitude fighter, powered by the DB 605A was given the GM-1 injection. The Fw 190A-3 was introduced with improved BMW 801D-2 engines providing more power. The Fw 190A-4 and Bf 109G-4 soon followed, with improved radios and homing devices. At their preferred altitudes – below 20,000 ft for the 190 and the reverse for the 109 -each of these types was a match for the Spitfire IX. Most of the fighters arriving at JG 2 and JG 26 bases in late 1942 were Bf 109s. The Fw 190 was in short supply, and given the multi-role function of the Fw 190 the Channel Front wings were to scheduled to revert to Bf 109s to permit the Fw 190 to move to priority theatres – a move encouraged by the Fw 190s lack of performance above 7,500 m (25,000 ft) where US bombers operated.