The British continued to develop indicator nets between World Wars I and II, though the Americans did not. In 1939, the British shared their expertise with the United States Navy. Before and during the attack on Pearl Harbor, Japanese midget submarines were able to enter the inner harbor via an open gate and avoid the submarine nets. The standard submarine net at Pearl Harbor consisted of 300 foot panels of 1 inch mesh rope with 8 foot diagonal openings. The midget submarines were designed to penetrate this type of net with features including a small size, net cutters and a tail with no projections which would snag the net. After the attack, a light indicator net was deployed at Pearl Harbor.
