Monument record MDO29763 - Royal Navy seaplane base, HMS Sereptia, Castletown, Portland

The First and Second World War seaplane base, HMS Sereptia, is located to the north of Castletown, Portland. Buildings and structures associated with the Second World War use of the site are visible on aerial photographs of the 1940s.

The site of a World War One seaplane base at Portland. It opened as HMS Sereptia in September 1916 and was taken over by the RAF in August 1918. After an inactive inter-war period the base became an active flying station again in 1939. After the war Portland became a helicopter development and training base which was moved to a new site to the west and commissioned as HMS Osprey in 1959. In 1999 the base was closed. During the First World War, a number of Short 184s, Fairey F16 Campania 2-seat coastal patrol seaplanes and a few converted Wright sea planes flew coastal patrols to protect shipping from German U-boat attacks. These were part of Number 241 Squadron of the RAF which comprised of three Flights; 416, 417 and 513. At the beginning of the Second World War the base was used by 771 Squadron, a Fleet Requirements Unit. Equipped with Fairey Swordfish and Supermarine Walruses, this Squadron towed targets for naval gunners to train on. For the rest of the war the base was held under Care and Maintenance and did not participate on active operations. After the war Portland became an important base for helicopter experiments and development and was commissioned HMS Osprey in 1959. A number of naval helicopter units were stationed there until the base was closed in 1999. Please refer to the source for more detailed information on squadrons and for photographs and plans of the site. <1> The harbour at Portland was one of a chain of Royal Naval Air Service seaplane bases to protect British shipping from U-boat attacks. The first shore base, HMS Serepta, was built in 1917. In 1939 772 Squadron was formed as a Fleet Requirements Unit at Portland and operated Swordfish floatplanes until July 1940. For the rest of the war Portland operated on a care and maintenance basis. After the war the Anti- Submarine School returned to Portland and the base was used for helicopter development work. The anti-submarine aircraft were replaced with helicopters and the base was moved to local playing fields where a landing ground, two blister hangars, operations centre and control tower were built. The base was the home for ship's Wasp flights and the local Search and Rescue helicopter service. The airfield was expanded in the 1960s and 70s with new hangars, workshops and fuel storage tanks being constructed. For a full list of the squadrons based at Portland please refer to the source. <2> The First and Second World War seaplane base, HMS Sereptia, is located to the north of Castletown, Portland. After the Second World War, the base was used as the Anti-Submarine School. It was commissioned as HMS Osprey in 1959. A number of naval helicopter units were stationed there until the base was closed in 1999 (see EHA record UID 1487063 for more details). Buildings and structures associated with the Second World War use of the site are visible on aerial photographs of the 1940s <3>. The structures consist of groups of buildings on the quayside and two jetties. A fuel store (MDO19665) is located to the west of the site and Phoenix Caissons can be seen moored offshore (see MDO6587-8 and MDO29764). This site was digitally plotted during the South West Rapid Coastal Zone Assessment Survey (Dorset).

Record last edited

Jun 9 2023 2:56PM