Type 97 torpedo

Not to be confused with Type 97 light weight torpedo (G-RX4).
Type 97 Special torpedo, run aground at Garden Island, Sydney

The Type 97 was a 17.7 inches (45 cm) diameter torpedo used by the Imperial Japanese Navy during World War II. Intended for use with Japan's Kō-hyōteki-class midget submarines, the torpedo was based on the 24-inch diameter Type 93 "Long Lance" used by Japanese surface vessels, but redesigned to meet the smaller 18-inch physical dimensions of the midgets' two torpedo tubes. Larger Japanese submarines were armed with the 21-inch Type 95 torpedo.

It was not a great success. Its first operational use was in the attack on Pearl Harbor, after which it was modified as the Type 97 Special, sometimes known as the Type 98. It had a 772 pounds (350 kg) warhead and a range of 3.4 miles (5.5 km) at 44 knots (81 km/h).