That's what we actually did, however RADAR was a new thing allowing a small number of British aircraft to regularly intercept Bombers. Without any evidence it must have seemed probable for something similar to be locating subs.
Detection worked just fine at night. The problem was: "Although the RAF control stations were aware of the location of the bombers, there was little they could do about them unless fighter pilots made visual contact." https://en.wikipedia.org/wiki/Radar_in_World_War_II
