Canada built HF direction finding units in Newfoundland. The stations would report the bearing they picked it up on, then a Convoy plotting room would take the bearings from a couple of stations and plot it, sending out coded signals to convoys in the area so they could alter to avoid the subs. I read a report that the smaller ships like corvettes had a hard time DFing signals as the rolled to much, creating to much uncertainty in the bearing.
If a good bearing was had on a sub nearby by a frigate or destroyer would run down that bearing to force the sub under. Corvette would do it, but struggled to catch up to the convoy that had altered course and increased speed.