Midget submarines have gotten a lot of press in recent years. The 2010 sinking of the South Korean corvette Cheonan by a North Korean Yono-class midget submarine showed that with today's modern torpedoes, they can pack a punch.
Midget submarines have arguably had a longer combat career than their bigger cousins. The Turtle, a one-man midget sub, was used in an effort to attack British ships off New York during the Revolutionary War.
The hand-powered midget submarine CSS Hunley successfully sank the sloop USS Housatonic in 1864. Larger coastal and fleet submarines didn't really achieve a lot of success until World War I.
Drawings of CSS Hunley. (Wikimedia Commons)
But the midgets still stuck around.
Nearly all the major powers used them in World War II. The British, Germans, and Japanese all had varying degrees of success with them.
The British X-boats managed to damage the German battleship Tirpitz. Japanese submarines had their high-water mark on May 29, 1942, when they damaged a British battleship and sank a merchant ship at Diego Suarez in Madagascar.
But Germany's Seehund — or "Seal" — was probably the most successful. Built in 1944, the Seehund displaced 17 tons, carried two torpedoes, and had a crew of two. The vessel could go four knots underwater, and seven knots on the surface.
U-Boat.net notes that 137 of these midget subs were commissioned, which sank eight vessels and damaged three more in four months of operation.
S 622, a German Seehund later taken into service by the French Navy. (Photo from Wikimedia Commons)
Below is a video showing how a replica of one of these mini-submarines was made for a museum display. Take a look and see what went into making that replica — and what that display will teach future generations about what life on one of these vessels was like.