My father was part of that. May 1943 marked the introduction of new very short wave radars for aircraft. Radar is a transmitter, and the outbound pulse can be detected a long way away. Far farther than the aircraft would see a return. The U boats had radar detector receivers. But they were made for the old, longer wave radars, so they never saw the planes coming.
Aircraft could find the U boats on the surface at night, and in the daytime when the plane was out of sight, above the clouds.
These radar units did not have the rotating line on a scope we see in the movies. The scope had a vertical line on it. The bottom of the line was close range, the top of the line was max range. If there was a signal, it would show as a fuzzy bulge on the line.
Dad's plane (RCAF Hudson) attacked 3 subs in three weeks as soon as they got the radar. By June the Uboat war was over.
In this picture, they had tracked the sub by radar and dropped down through light cloud to discover they had been tracking the snorkel, and as luck would have it, as they got there, the sub was surfacing. In the original picture you can see the
conning tower crew looking up in surprise as they were about to receive a perfect straddle attack. The sub had two deck guns, an unusual feature, so it was not difficult to identify. Picture was taken with a hand held K20 camera, with a yellow filter.