The equipment war had changed also. The newer types of P-47Ds and Ns and the North American P-51 MustangD were superior to the Fw 190 and Bf 109 variants then in service at high-altitudes. The Luftwaffe began to develop high-altitude variants in response, but the Fw 190 D, meant as an interim solution until the arrival of the Focke-Wulf Ta 152, did not appear until late 1944. The Bf 109 was reaching the end of its development potential. The Bf 109 G-10 could not accommodate an engine large than the DB 606D. The G-10 did receive the GM-1 additive to the supercharger which allowed for better high-altitude performance. The G-10 had only one 20mm gun, with two 13mm machine guns to keep it light. The arrangement gave the fighter a speed of at . By the spring, 1944, the quality and numbers of USAAF fighter escorts led to heavy casualties among the German fighter force which no training organisation could cope with. The losses in the first four months were equal among American and German formations, but the Luftwaffe was losing the qualitative war. Galland reported in late April, that since the beginning of the year, 1,000 German pilots had been lost, including the best "Staffel", "Gruppe", and "Geschwader" commanders. He remarked the time had come when the German fighter arm "was in sight of collapse." In February 1944 JG 1 began improving its high altitude capability by replacing the Bf 109 G-5 and G-6s GM-1 equipment, with Bf 109 G-6/AS high altitude fighters with DB605AS engines which were formed into "Höhengruppen" [high-altitude] "gruppen". III./JG 1 received this type. The German jet projects, the Messerschmitt Me 262, He 162, rocket aircraft Messerschmitt Me 163, and Push-pull configuration Dornier Do 335; only the Me 262 was due to enter service by May 1944. JG 1 would operate one of these types—the He 162—in the closing weeks of the war.