Pre-war preparation did not remove ASDIC's limits

Did the Royal Navy fail to foresee the submarine threat before the Second World War?

No. It prepared seriously, though exercises encouraged overconfidence in ASDIC and war began before every planned measure was in place.

Interwar navies did not simply fail to anticipate submarine warfare. The Royal Navy had a large, technologically capable submarine service, and many senior officers had served in it. British submarines worked in the Mediterranean and North Sea, often on intelligence and monitoring duties that produced fewer spectacular headlines than merchant-shipping campaigns. The service also planned escort numbers and operating methods around the expectation that several ships might be needed to prosecute one submarine. Exercises nevertheless reinforced confidence in ASDIC beyond what combat would justify, an example of trials producing confirmation bias. Fair assessment therefore requires looking at what services were planning and building, rather than only the incomplete forces present when war arrived unexpectedly for every major navy.