Deck gun is great pre 1942 but after that everywhere bar Cape Hatteras ships are armed and one good hit destroys any hope of keeping 100% hull integrity for 220+ metres crah dive depth to avoid HK groups. Even shooting at night at crippled ships with a crack gun crew from 2500+ metres plus is risky. Dido class take 1 torpedo. Revenge class take 3. The Ark Royal took 2. HMS Nelson off Norway took 7. A 4000 tonne merchant should need one and then founder and sink over the following hour. Not 2+ gunfire. Think I'll just miss em out. Passenger cargoes are no problem at all. One torp and gone within 30 minutes.
Riccardo. U-501