The Underwater Demolition Teams (UDT) were a special-purpose force established by the United States Navy during World War II. They came to be considered more elite and tactical during the Korean and Vietnam Wars. Their primary WWII function began with the reconnaissance and removal of natural or man-made obstacles on beaches prior to amphibious landings. They later were assigned to assist in the recovery of Space capsules/astronauts after splash down in the Mercury and Apollo space flight programs. The United States Navy's Underwater Demolition Teams were pioneers in underwater demolition, closed-circuit diving, combat swimming, and midget submarine (dry and wet submersible) operations. Commando training was added making them the forerunner to the United States Navy SEAL program that exists today.
In 1983, after additional SEAL training, the UDTs were re-designated as SEAL Teams or Swimmer Delivery Vehicle Teams (SDVTs). SDVTs have since been re-designated SEAL Delivery Vehicle Teams.