US Navy (USN) Aviation Warfare Systems Operator Third Class (AW3) Garrette Keller, assigned to the "Black Knights" of Helicopter Anti-submarine Squadron Four (HS-4) mans a 7.62 mm M240D machine gun aboard a SH-60 Seahawk while acting as plane guard for the Nimitz Class: Aircraft Carrier, USS RONALD REAGAN (CVN 76), and embarked Carrier Air Wing One Four (CVW-14) while the ship is underway conducting Tailored Ship's Training Availability (TSTA) in the Pacific Ocean

Aircraft carriers are warships that act as airbases for carrier-based aircraft. In the United States Navy, these consist of ships commissioned with hull classification symbols CV (aircraft carrier), CVA (attack aircraft carrier), CVB (large aircraft carrier), CVL (light aircraft carrier), CVN (aircraft carrier (nuclear propulsion) and CVAN (attack aircraft carrier (nuclear propulsion). The first aircraft carrier commissioned into the United States Navy was USS Langley (CV-1) on 20 March 1922.