Conversion of Sherman tanks to the Sherman Firefly (a Sherman tank fitted with the 17-pounder gun) was significantly faster than Challenger production and driven by operational needs of the Normandy invasion, production of Challenger was dropped. Fireflies (and the limited number of Challengers) provided additional firepower to Cromwell and Sherman armed troops. One Firefly would be issued to each troop of Cromwells (giving three Cromwells and one Sherman Firefly). Problems were encountered due to the different maintenance requirements and associated supply complication of two tank models, as well as the performance difference between Cromwell and Sherman and the Sherman's silhouette, even larger than the Challenger. The large size and obvious difference of both Challenger and Firefly made them a priority target for Axis forces.