Japan's thin submarine patrol off the West Coast

I-17 belonged to the seven-submarine patrol sent toward the American West Coast during the Pearl Harbor operation. The boats probably sank two merchant ships, damaged six more, and twice encountered American air or surface forces. All seven returned to friendly waters, and some, including I-17, returned to American waters after resupplying at Kwajalein. A counterfactual alternative would divert resources from Yamato and Musashi toward carriers, cruisers, and more long-range submarines. Britain's initial wartime shift toward small vessels later created difficulties when the fall of Norway and France increased the need for larger ships. American construction emphasized battleships and carriers without a comparable investment in small Flower-class-scale escorts. The limited Japanese patrol and the American escort shortage both reflected choices about which ships to build.