As I recall.. only the merchie's had them... part of the convoy agreement between other countries & the Brits. Was a... signifier of them being attacked, as if the sight of a fireball from some, wasn't enough of a road flare sign of an attack...
Warships, wouldn't use that... their whole... purpose, was to sail into harm's way... merchie's, weren't. Theirs, was to deliver the goods...
Which, made them, prime targets for the U boats... but.. the U.S., went with unrestricted targeting, after Pearl got hit... & turned on Japan, what was Britain's (& Churchill's, worst nightmare of happening to them) into Japan's worst nightmare... being brought to their knees by being strangled out of resources.
That... & the A bomb.
M. M.