That's a P-38 Lightning, arguably the second best fighter the USA had in WW2, second only to the P-51 Mustang.
The firepower was impressive and was comprised of one 20MM cannon and four .50 caliber machine guns.
Known by the German Luftwaffe as "Der Gabelschwanz Teufel" (The Fork-Tailed Devil) and to the Japanese as "two planes, one pilot", the P-38 Lockheed Lightning was light years ahead of its time. Designed as a high-altitude interceptor and contrary to what some think, the P-38 was not just a fighter; it also carried high explosive and incendiary bomb loads -- competingwith the early WWII bomber aircraft (with bomb loads of up to 4000 pounds). It was the fighter of choice for pilots.
Approximately 10,000 P-38's were built, and they flew in every combat theater, around the world during WWII.