Why The U.S. Military Only Ever Built & Used One Midget Submarine
When the Japanese attacked Pearl Harbor on December 7, 1941, they did so with all kinds of aircraft and naval vessels. The daring attack also utilized five Japanese midget submarines — which, as the name implies, are smaller than standard subs. The purpose of a midget submarine in combat is harbor penetration: Moving into the shallower waters of a harbor where the sub and its occupants can wreak havoc upon the enemy. The Japanese did this often and with some success throughout WWII.
The United States, on the other hand, never used midget submarines in combat. Most American combat vessels were significantly larger, and there wasn't a strategic need for midget submarines in the fight against Imperial Japan. Midget submarines are technically any sub that displaces 150 tons of seawater or less. That's incredibly small for a sub, as the standard American submarine used in World War II — the Gato-class — displaced over 10 times as much seawater with a complement of 60 personnel.
While it wasn't U.S. policy to build and operate midget submarines, one was built long after the war. The SS X-1, which never received an official name, was first launched in 1955 for the purpose of testing harbor defenses. Essentially, the Navy wanted to train its personnel on defending a harbor from a midget submarine, so one was constructed for that purpose. The X-1 proved to be useful and was a success, though it didn't remain in active service for long.
[Featured image by U.S. Navy via Wikimedia Commons | Cropped and scaled | Public Domain]
Though intended for defense, the SS X-1 never moved on from testing
The SS X-1 was built by an aerospace manufacturing company in an airplane hangar. When it was completed, it weighed in at only 36.3 tons submerged, so it was considerably smaller than most American submarines. The diminutive boat stretched for 49 feet and 7 inches, and had just enough room inside for its crew complement of five submariners. The X-1 wasn't armed, as it was never intended for combat and was only used for research, training, and testing.
When it was built, the X-1 ran on a hydrogen peroxide diesel engine with accompanying batteries. In May 1957, an explosion of its fuel resulted in a conversion to a standard submarine diesel-electric engine, but it left active service by December of that year. The X-1 moved to Philadelphia, where it remained for a few years before making its way to Annapolis and the Chesapeake Bay, where it was reactivated and operated by Submarine Squadron 6 to test harbor defenses against potential Cold War invasions.
When its tests were completed, the X-1 was retired from active service and transferred to the Naval Ship Research and Development Center in 1973. The X-1 did what it was constructed for, and there was no longer any need to maintain a midget submarine (or build others). It was designated a museum ship, and in 2001, it was transferred to the Historic Ship Nautilus & Submarine Force Museum in Groton, Connecticut, where it can be visited. The museum's collection includes the USS Nautilus (SSN-571), three midget submarines, and similar naval exhibits.
[Featured image by Z22 via Wikimedia Commons | Cropped and scaled | CC BY-SA 3.0]