 The ability to verify British claims against the British ' main opponents in 1941 and 1942 , JG 26 and JG 2 , is very limited . Only two of the 30 volumes of War Diaries produced by JG 26 survived the war . Historian Donald Caldwell has attempted to use what limited German material is available to compare losses and air victory claims but acknowledges the lack of sources leave the possibility for error . 
