Naval deck guns.
Jutland 1916 deja vu?
Captain Rogge at the helm if you please!
Armed merchantmen also in the ancient and venerable manner carrying naval deck guns. NOT guns in turrets with a barbette, nonetheless a quick-and-dirty and effective means of adding firepower to the commercial vessel?
German WW2 88 mm [3.5 inch] naval deck gun with shield. Fast direct fire weapon with flat trajectory for ease of aiming. I imagine a naval deck gun mounted on a merchantman would look somewhat like this.
British four-inch [100 mm] naval deck gun. Base mounted to the deck of the ship.
Five-inch [127 mm] naval deck gun.
Six-inch [152 mm] naval deck gun with shield. The famous WW2 era German surface raider Atlantis as captained by Rogge had six of these guns on board. That shell alone weighs 100 pounds [45 kilograms] and gives you some significant range and hitting power.
Is it beyond belief that a return to the olden days will occur? Deck guns having at least some sort of purpose in the modern age, shore bombardment and the like.
And where to obtain such ordnance? Mothballed somewhere, vessels antiquated having no further usefulness but their deck guns still a viable option for the armed merchantman?