For three years she provided a scheduled weekly cargo feeder service linking Union-Castle liners that terminated at Southampton with the German ports of Bremen and Hamburg.

[3] She was a motor ship with an eight-cylinder two-stroke single-acting diesel engine that was rated at 539 NHP[3] and gave her a service speed of 14 knots (26 km/h).

[1][4] Walmer Castle replaced the 1,236 GRT Eider, a steamship launched in 1900 that Union-Castle had acquired in 1926 from the Royal Mail Steam Packet Company.

After France capitulated in June 1940 Walmer Castle carried cement to UK ports to build fortifications against the threat of invasion.

[5] In August 1940 the Admiralty requisitioned Walmer Castle as an armament supply ship and sent her to Scapa Flow,[5] where she arrived in ballast on 11 September in Convoy WN 14 from the Firth of Clyde.

Convoy rescue ships were called Mercantile Fleet Auxiliaries, had a Merchant Navy crew and flew the blue ensign.

[7] Walmer Castle's first deployment as a rescue ship was with Convoy OG 74, which left Liverpool on 12 September 1941 bound for Gibraltar.

The next day Walmer Castle was 700 miles west of Ushant and had not yet caught up OG 74 when a Focke-Wulf Fw 200 Condor of Kampfgeschwader 40 came out of the sun and attacked her.

Walmer Castle's DEMS gunners opened fire on the incoming aircraft and the Master, Gerald Clarke, sharply changed the ship's course, which ensured that the Fw 200's first bomb missed.

It the fourth attack run a bomb from the Fw 200 destroyed the starboard wing of the bridge, killing Captain Clarke, and penetrated the engine room.

Survivors from City of Waterford, Empire Moat and Baltallin and wounded crewmen were put on life-rafts and in number three starboard lifeboat.