The Blenheim was one of the first British aircraft with an all-metal stressed-skin construction, retractable landing gear, flaps, a powered gun turret and variable-pitch propellers. The Mk I was faster than most fighters in the late 1930s but the advance in development of monoplane fighters made all bombers more vulnerable particularly if flown in daylight, though it proved successful as a night fighter. The Blenheim was effective as a bomber but many were shot down. Both Blenheim types were used by overseas operators, being licence built in Yugoslavia and Finland.