France builds around Surcouf while Japan reaches toward the I-400

France's allowance would likely support roughly six or seven large boats, with Surcouf providing the obvious starting point for weapons and employment. Japan has a stronger geographic incentive to pursue the range and specialized capabilities later associated with the I-400 class. From the opening of war those boats could operate near the Panama Canal or the American West Coast. Even when they caused limited physical damage, the threat would force the United States to divert ships, aircraft, and coastal defenses away from other missions.