Last night I took out a troop ship and an ore carrier. The troop ship ate a volley of 4 torpedoes, which I sent to her graciously. But the ore carrier took three shots at its engine room.
With the newer versions of GWX it feels that anything larger than a small merchant is now very heavily armored and requires multiple torpedos to neutralize. Usually, one shot in the engine room used to be pretty much devastating for any medium merchant.
Even battleships never take more than four torpedoes.
I don't expect one shot kills while aiming at the engine room but one well placed shot there should slow it down to a crawl atleast. But thats not happening anymore.