"Narwhal"

Unicorn was considered, Narwhal was overwhelmingly deemed better. Ah, the '50s...

Boasting a cannon

with a whopping 45mm caliber on its nose, the Narwhal is surely an interesting aircraft. Along with its cannon, it has four .50 caliber machine guns, for secondary fire in case of an emergency. Although the Narwhal is a well-potent fighter, it's actually an interceptor, sometimes even called a bomber destroyer due to its immense firepower. Be wary when fighting the Narwhal, it may not be the top-tier aircraft in terms of performance, but it's good enough to hold its own, and that 45mm cannon will obliterate fighters and bombers alike. Cannons don't discriminate.
Also yippee, FSF naval fighters that actually look remotely naval (not just the paint scheme, AG1 and AG2 respectively trigger the arresting hook and wing fold)

Trivia

-I found a thing.
-Despite the letter-number designation of the Narwhal, it has no lore-based relationship to my FI-series aircraft (e.g. FI-28, FI-63, FI-90). FSF isn't in the same universe as Combined SimpleVerse.
-A Narhwal once accidentally shot a friendly B-29 mistaking it for a Tu-4. By some miracle, the 45mm shell only blew off the wingtip, so both planes and their crew returned home safely. However, it's probably for the better this happened anyways; the B-29 was close to enemy lines, and if the Narhwal hadn't shot it, something else probably would've.
-An attack version of the FI-5 was planned which had a 76mm anti-tank gun mounted in the nose instead of the 45mm anti-bomber cannon. One prototype flew, but was never put into service.