A seaplane tender (or seaplane carrier) is a ship which provides the facililites necessary for operating seaplanes. These ships were the first aircraft carriers and appeared just before the First World War - the first being HMS Hermes , and old cruiser converted and commissioned in 1913. They had hangars for storing and maintaining the aircraft, but no flight deck as in a true aircraft carrier. Instead they used cranes to lower the aircraft into the sea for takeoff and to recover them after landing.

The ships were normally converted merchant vessels rather than specially constructed for the task. As aircraft improved the problems of using seaplanes became more of a handicap. The aircraft could only be operated in a smooth sea and the ship had to stop for launching or recovery, both of which would take around 20 minutes. The tender was often stationed ten miles or so in front of the main battle fleet with the cruiser screen so that it would not fall hopelessly behind when it launched its aircraft. Seaplanes also had poorer performance than other aircraft because of the drag and weight of the floats. Seaplane tenders had largely been superseded by aircraft carriers in the battle fleet by the end of the First World War, although aircraft were still of minor importance compared to the firepower of naval artillery.

In the inter-war years, it was common for cruisers and battleships to be equipped with catapult-launched reconnaissance seaplanes, but by the end of the Second World War the availability of aircraft carriers and the performance of their aircraft meant that most of these ships had their catapults removed and the hangars converted to other purposes.

Seaplane tenders continued to be used until after the end of the Second World War, although usually as support vessels which operated seaplanes from harbours rather than in a seaway. These aircraft were generally for long range reconnaissance patrols. The tenders allowed the aircraft to be rapidly deployed to new bases because their support facilities were mobile, in a similar way to depot ships for submarines or destroyers and runways did not have to be constructed. A few remained in service after the war but by the late-1950s most had been scrapped or converted to other uses such as helicopter repair ships.

Seaplane tenders included:

• HMS Ben-my-chree was a converted ferry used in the First World War
• HMS Engadine was another converted ferry present at the Battle of Jutland
• USS Langley (CV-1) was the United States' first aircraft carrier, but converted from an aircraft carrier to a seaplane tender in 1937
• USS Mississippi (BB-23) was an obselete battleship used as a seaplane tender in 1914.