Hellcat was the name of both an American carrier-borne fighter aircraft, and an American tank destroyer. Firefly was the name of both a British carrier-borne fighter aircraft, and a British (mainly) tank destroyer. Almost all of them had their combat debut in 1944 (only the Grumman F6F Hellcat already in September 1943). Is this entirely coincidential, or has there been any influence in any direction? Like, some Englishman said: "Hey, they Americans called their new tank destroyer design like one of their naval fighters. Let's do the same! What's our most current type? The Fairey Firefly? So let's call our new Sherman-based anti-tank design Firefly!"