Anti-submarine warfare and submarine warfare developed together. A navy cannot learn how to counter an opponent's boats without understanding what its own submarines can do, and foreign navies will not normally supply their best submarines for exercises. Domestic submarines therefore served as both operational weapons and demanding test opponents for escort crews. Wartime crews would accept risks that peacetime exercises understated.
Notable Point · 5:41-7:23
Building submarines to improve anti-submarine warfare
The Navy needed capable submarines of its own to give its escorts realistic opponents and expose weaknesses in ASW tactics.