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 run, so the number of Panthers deployed came as a surprise to Allied formation commanders and tank crews forced to engage them with guns that could not penetrate the frontal armour except at short range.