 An escort could then run in the direction of the signal and attack the U-boat, or at least force it to submerge (causing it to lose contact), which might prevent an attack on the convoy.When two ships fitted with HF/DF accompanied a convoy, a fix on the transmitter's position, not just direction, could be determined.The British also made extensive use of shore HF/DF stations, to keep convoys updated with positions of U-boats.