Airborne radar was a major U-boat killer

Was HF/DF, sonar, or radar the most important Battle of the Atlantic technology?

HF/DF and sonar were critical, while airborne radar was especially important because it let aircraft find and attack U-boats.

HF/DF and ASDIC or sonar each made an important contribution. Direction finding helped locate transmissions, while sonar mattered for prosecuting underwater contacts. Radar, especially airborne radar, was a consistent killer because it let Swordfish and other patrol aircraft close on surfaced or exposed submarines. The comparison ties each technology to a different part of convoy protection and U-boat vulnerability.