The Admiralty modified Seraph at Devonport to raise her underwater speed and approximate the performance problem posed by the German Type XXI. Anti-submarine forces then exercised against her in September and October 1944. Those trials indicate that the Allies knew enough about the Type XXI to investigate counters before it became an operational shock. This did not make the new boat easy to defeat, but intelligence and experimentation had already framed the problem.
Notable Point · 1:13:15-1:14:49
Seraph simulates the Type XXI for Allied anti-submarine trials
The Royal Navy modified Seraph for higher underwater speed so anti-submarine forces could rehearse against a boat approximating the German Type XXI.