This is coolbert:
Capture, high seas! Tit-for-tat.
Here with an aspect of submarine warfare as waged during the Second World War [WW2] I was not familiar with.
British capturing a German submarine [U-570] and incorporating same into the inventory of the Royal Navy. Germans capturing a British submarine [HMS Seal] and incorporating same into the inventory of the Kriegsmarine.
1. HMS Graph. Formerly German U-570.
"HMS Graph (pennant number P715) was a German Type VIIC U-boat that the British Royal Navy captured during World War II. Commissioned as U-570 in Nazi Germany's Kriegsmarine in mid-1941, she was attacked and captured on her first patrol."
"She [U-570] provided both the Royal Navy and United States Navy with significant information on German submarines, and carried out three combat patrols with a Royal Navy crew, becoming the only U-boat to see active service with both sides during the war. She [HMS Graph] was withdrawn from service in 1944 due to problems maintaining her."
2. German U-B. Formerly HMS Seal.
"U-B. The former HMS Seal commissioned as U-boat U-B . . . U-B was of limited value to the Kriegsmarine except for training and propaganda purposes. Analysis of her British torpedoes led to development of a superior pistol design (torpedo detonation device) to replace the existing highly unreliable [German] type."
THE BIGGEST HURDLE WITH SUCCESSFULLY INCORPORATING AN ENEMY VESSEL INTO YOUR OWN NAVY IS SPARE PARTS! SURELY THE CASE IN THESE TWO INSTANCES. COMBAT CAPABILITY SEVERELY LIMITED AS A RESULT!