For the Luftwaffe, the winter, 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 109 G-1 high-altitude fighter, powered by the DB 605A was given the GM-1 injection. The Fw 190 A-3 was introduced with improved BMW 801D-2 engines providing more power. The Fw 190 A-4 and Bf 109 G-4 soon followed, with improved radios and homing devices. At their preferred altitudes – below for the Fw 190 and the reverse for the Bf 109 -each of these types was a match for the Spitfire IX.