While armed merchantmen weren't particularly effective at actually fighting U-Boats, the mere act of arming them had a tactical and strategic effect. The Battle of the Atlantic could be won by hampering U-Boat attacks as much as sinking U-Boats.
U-Boats are not really submarines, they're submersibles; they spend most of the time on the surface. Underwater ...
Were armed merchantmen effective against submarines?
They were called Q-Ships short for Queen Ships armed Merchantmen which convoyed with the merchant fleets for protection. No they weren't very effective.
The German's had 13, British employed 9, the United States beginning in January 20, 1942 outfitted 5 in the Atlantic and 1 in the ...
I suspect that, less than an absolute "solution" or match, the usefulness was in limiting U-boats' tactical options:
deck guns. Early ww2 U-boats had guns and liked to use them - saved on torpedoes among other things.
surface, rather than submerged stalking and attacking. U-boats, until the Schnorkels came along (too late to do much), ran on batteries ...
Armed merchantmen could clearly deal with a submarine attacking by day, on surface.
During the night, U-Boats surface attacks would include many submarines, and the capacity of numerous merchantmen to defend a convoy would clearly be about the tactical plot:
Who would detect first?
Detect before the launch of torpedoes?
And in ...