During WWII there was somewhat surprizigly unified ship classification and there was hardly any civillian submarines at the time. It was based on tonnage, speed

During WWII there was somewhat surprizigly unified ship classification and there was hardly any civillian submarines at the time. It was based on tonnage, speed and main gun calibre. Anything smaller than 1000 tons was a boat. Interwar German submarines we're around 500 - 1000 tons, so they we're called "u-boot". Since WWII names stuck by role of ship. Now we have all kinds of propaganda pieces floating around and ship classification names don't mean anything anymore. A "frigate" might be anything except oil tanker or CATOBAR carrier. If you would use WWII classification by top speed and tonnage and apply it to modern vessels, Ohio class submarine would be "Submarine Heavy Cruiser" and Typhoon would be "Submarine Battleship".