Before they become instruments of war, they sound like impossible ideas; an American medical student develops a closed-circuit rebreather that allows Allied frogmen to slip beneath enemy harbors without a single bubble, while U.S. Army engineers create a jeep-mounted nuclear launcher known as the "atomic watermelon"; across the Atlantic, an inventor pitches an aircraft carrier to hunt U-boats, carved from wood pulp and ice; because in war, today's absurdity can become tomorrow's secret weapon.