parts for two different tanks. The Firefly was also slower than the Cromwell. Churchill units received no Fireflies, and as a result often had to rely on any attached M10 or M10 Achilles units to provide increased firepower to deal with tanks their own guns could not eliminate. Production was limited by the availability of suitable tanks, with the phasing out of 75 mm Sherman production. To make up numbers, Sherman I and Sherman I Hybrids were also converted. From D-Day in June to the end of the Battle of Normandy in late August, almost 400 Sherman Fireflies were converted, more than sufficient to replace any permanent tank losses during the battle. In late 1944, with the creation of an effective high-explosive shell for the 17-pounder gun, British units started to receive two Fireflies per troop. By February 1945, some 2,000 Sherman Fireflies had been built and British, Commonwealth and Polish armoured units were equipped with a 50/50 mix of 75 mm and 17-pounder-armed Shermans. In the spring of 1945, production of the Firefly was scaled down, with the last tank being delivered in May 1945. This was the result of several factors, from superior home-grown designs like the Comet and Centurion coming into service to replace the Firefly, to the impending defeat of Nazi Germany, and the inferior design of Japan's tanks, which it seemed would be the next opponents the British would have to face after the fall of Germany. Production of the Sherman Firefly reached some 2,100 – 2,200 tanks; exact numbers are hard to determine as documents give contradictory totals. Jane's World War II Tanks and Fighting Vehicles gives a production of 1,783 vehicles in 1944 and 563 in 1945, for a total of 2,346. Sherman Firefly gives a number of 2,002 conversions made between January 1944 and February 1945 or a total of 2,139 conversions. Service Normandy Fireflies were introduced to armoured brigades and divisions in the 21st Army Group in 1944, just in time for the Normandy landings. The timing was fortunate as Allied intelligence had begun to realise in early 1944 through statistical analysis that the Germans were fielding a much larger number of more formidable tanks (such as the Panther) than had been anticipated. This information was slow to reach Allied military planners, who had mistakenly assumed the Panther, like the Tiger, would be a rare heavy tank with a limited production