After the difficult problem of getting such a large gun to fit in the Sherman's turret was solved, the Firefly was put into production in early 1944, in time to equip Field Marshal Bernard Montgomery's 21st Army Group for the Normandy landings. It soon became highly valued, as its gun could almost always penetrate the armour of the Panther and Tiger tanks it faced in Normandy, something no other British Army tank could reliably do at that time. In recognition of this, German tank and anti-tank gun crews were instructed to attack Fireflies first. Because the Firefly had a visibly longer barrel, crews tried to camouflage it so the tank would look like a normal 75 mm-gun Sherman from a distance. Between 2,100 and 2,200 were manufactured before production wound down in 1945.