The U.S. Narwhal and Nautilus displaced nearly 4,000 tons submerged and mounted the largest guns carried by American submarines. Japan's four J1 boats combined six bow and two stern tubes with a twenty-torpedo load, demonstrating how much weaponry a large hull could carry. I-1 later took part in the Pearl Harbor operation and yielded about 200,000 pages of codes, charts, manuals, and logs when salvaged by the U.S. Navy. Italy's lighter Ettore Fieramosca used a 4.7-inch gun and enough submerged speed to negotiate the Strait of Gibraltar, showing that the category could also be adapted to Mediterranean geography.
Chapter · 8:23-11:37
American, Japanese, and Italian cruiser submarines
Contemporary American, Japanese, and Italian boats show that large, heavily armed ocean-going submarines were an international interwar category.