During 1942, handling and performance trials were first undertaken at RAF Boscombe Down. By 1944, the Firefly had been cleared to use underwing rocket projectiles and, by April 1944, tests involving a double-underwing load of 16 rockets and a pair of drop tanks still provided acceptable handling. Further testing with two 90 gallon (410 l) drop tanks or two bombs deemed acceptable albeit with "...a small adverse effect on handling..." while "...handling with a single bomb was unpleasant, but manageable." Performance trials at indicated a maximum speed of at while a climb to took 12.4 minutes, with a maximum climb rate of at , and a service ceiling of .