There were several submarines with large mounted guns which would see service between the First and Second World War. The first of these were the British 'M'-class submarines. They were designed in 1915-16, following worries that the Germans might use submarines with a heavy gun armament for coastal bombardment. The design studies for a British equivalent, either with a 12in gun or one-two 7.5in guns, provoked thought that such a submarine would also be useful for anti-shipping work. A torpedo was slow, and hence inaccurate against manoeuvring warships, especially at range, while a shell would be more accurate. As such, their role changed to reflect this concept. Four boats were ordered in 1916, but only three would be completed, given the names M 1-3. Of the gun-armed submarines, these most closely reflect the one you were thinking of. They mounted a single 12in gun, taken from obsolete predreadnought battleships, in a mounting forward of the sail. The gun could be trained 10^o in either direction, elevated to 20^o and depressed to 5^o . In addition to this, they had a single 3in AA gun, and four torpedo tubes (18in on M 1 and M 2, and 21in on M 3). The 12in gun could be fired while the submarine was submerged, using a procedure called the 'dip-chick'. The submarine's depth was adjusted such that the gun muzzle was 6ft out of the water, the gun aimed by periscope and fired, and then the boat would submerge. It would then break contact, and surface to reload - the gun could only be reloaded on the surface. Of the three completed boats, only M 1 would retain the gun for the whole of her time in the navy, being lost in an accidental collision in 1925. M 2 had her gun removed, and replaced with a hangar for a small seaplane. She was lost in an accident while surfacing in 1933. M 3 was converted to a minelayer, and provided useful experimental experience while the RN was designing the Porpoise class of minelaying submarines, before being scrapped in 1932.

In the interwar period, submarines with a heavy gun armament were designed and built by most of the major navies. Known as 'cruiser submarines', they were motivated by a desire to build submarines for merchant raiding that could follow the strictures of international law (which I have discussed here). These required submarines to spend a significant amount of time surfaced to search and sink merchant ships. A surfaced submarine would be vulnerable to escorts, but one with a heavy gun armament would be able to fight them off. The Germans had provided a number of inspirations during WWI, with the three boats of the U-139 and seven of the U-151 classes. These had two 5.9in guns in open deck mounts in addition to their torpedo armament, and saw fairly successful service over the course of the war. In 1923, the British launched an experimental cruiser submarine, the X 1. This was armed with four 5.2in guns in twin mounts fore and aft of the sail. She was fairly successful in her designed role, but was greatly let down by her unreliable engines. She was scrapped in 1936 and would not be followed by any successors. The Japanese commissioned four cruiser submarines of the I-1 class from 1924. Like the German boats, they had two 5.5in guns in open mounts. These would survive to see service in WWII, as would their American counterparts. The American boats were originally called V-4, V-5 and V-6 when commissioned in 1928-30, but would be renamed to Argonaut, Narwhal and Nautilus in 1931. All three had two 6in guns in open mounts, though Argonaut was primarily designed as a minelayer. The French built the last, and largest, of the cruiser submarines, the Surcouf. This had two 8in guns in an enclosed mount forward of the sail, as well as a floatplane and ten torpedo tubes. Launched in 1929, she would see service in WWII. She was in the British port of Plymouth after Fall of France in 1940, where she was taken into the Free French Navy after a brief firefight in her control room where three British sailors and one Frenchman were killed. After a refit, she was sent to Canada, where she liberated the French islands of St Pierre and Miquelon, before vanishing while being sent to the Pacific in early 1942. She was likely sunk in an accidental collision with a merchant ship.