The Royal Naval Air Service (RNAS) was the air arm of the Royal Navy until near the end of World War I.

When the Royal Flying Corps (RFC) was founded on April 13, 1912 it was intended to encompass all military flying. The Navy however was not pleased at all forms of naval aviation being moved to an Army corps. It soon formed its own, unauthorised, flying branch with a training centre at Eastchurch. The Admiralty had enough political clout at that time to ensure that this act went completely unchallenged. The Royal Naval Air Service was officially recognised on July 1, 1914.

By the outbreak of the First World War in August 1914, the RNAS had more aircraft under its control than the Royal Flying Corps. It maintained twelve airship stations around the coast of Britain from Longside, Aberdeenshire in the north east to Anglesey in the west. The main roles of the RNAS were fleet reconnaissance, patrolling coasts for enemy ships and submarines, attacking enemy coastal territory and defending Britain from enemy air-raids. Later in the war, squadrons of the RNAS were sent to France to directly support the RFC.

Before techniques were developed for taking off and landing on ships, the RNAS had to use seaplanes in order to operate at sea. Beginning with experiments on the old cruiser HMS Hermes, special seaplane tenders were developed to support these aircraft. It was from these ships that a raid on Zeppelin bases at Cuxhaven and Wilhelmshaven was launched on Christmas Day of 1914. This was the first attack by ship-borne aircraft. A chain of coastal air stations was also constructed.

The leading RNAS WWI ace was Raymond Collishaw with 60 victories.

On April 1, 1918 the RNAS, which at the time had 67,000 officers and men, 2,949 aircraft, 103 airships and 126 coastal stations, was merged with the RFC to form the Royal Air Force.

The Royal Navy regained its own air service in 1937 when the Naval Air Branch was returned to Admiralty control. It was renamed the Fleet Air Arm.

Some members of the RNAS

• Henry Allingham - Mechanic - oldest British veteran
• Richard Bell-Davies - 3 Squadron - Victoria Cross winner
• Henry John Lawrence Botterell - Naval 8 - last living WWI figher pilot
• Raymond Collishaw - 10 Naval - top RNAS ace
• Christopher Draper - 3 Wing, 6 Naval, Naval 8 - "The Mad Major"
• Bert Hinkler - Australian aviation pioneer
• James White - Naval 8 - ace