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Osea Island, Essex: Secret Naval Base at a Secret Island

The hive of activity unbeknown to the Essex community

Tucked in the mouth of the River Blackwater, Osea Island is remote, secluded and secretive. During World War One, the island was the perfect location to station dozens of torpedo-carrying speedboats.

Run by hundreds of sailors and Women’s Royal Naval Service (WREN) personnel, the base was called HMS Osea and was a hive of activity – virtually unbeknown to those living on the Essex coast which surrounded them.

The craft were called coastal motor boats or CMB’s, between 40ft and 70ft in length, capable of carrying up to two torpedoes or four depth charges. Their small design gave them a top speed of 30kts and great manoeuvrability.

The CMB’s were initially stationed in Kent but were too visible, so the decision was taken to move them to Osea Island. Its location proved to be one of its greatest assets – protected by land on three sides, yet able to be in the North Sea in a matter of minutes, as historian and author Julian Foynes explains.

Location: Osea Island, Essex CM9 8UH
Image: Some of the WRENs working at the Manor House on Osea Island, which still stand today. Photograph courtesy of Imperial War Museums.

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