HMS Avenger was a Royal Navy escort aircraft carrier during the Second World War. In 1939 she was laid down as the merchant ship Rio-Hudson at the Sun Shipbuilding & Drydock Company yard in Chester, Pennsylvania. Launched on 27 November 1940, she was converted to an escort carrier and transferred under the lend lease agreement to the Royal Navy. She was commissioned on 2 March 1942.

The escort carrier or escort aircraft carrier, also called a "jeep carrier" or "baby flattop" in the United States Navy (USN) or "Woolworth Carrier" by the Royal Navy, was a small and slower type of aircraft carrier used by the Royal Navy, the Royal Canadian Navy, the United States Navy, the Imperial Japanese Navy and Imperial Japanese Army Air Force in World War II. They were typically half the length and a third the displacement of larger fleet carriers, more-lightly armed and armored, and carried fewer planes. Escort carriers were most often built upon a commercial ship hull, so they were cheaper and could be built quickly. This was their principal advantage as they could be completed in greater numbers as a stop-gap when fleet carriers were scarce. However, the lack of protection made escort carriers particularly vulnerable, and several were sunk with great loss of life. The light carrier was a similar concept to the escort carrier in most respects, but was fast enough to operate alongside fleet carriers.