UDT meaning in General ?

Underwater Demolition Teams (UDT) had a specialized non-tactical mission when the United States Navy created them during World War II. Postwar they transitioned to scuba gear changing their capabilities. With that they came to be considered more elite and tactical during the Korean and Vietnam Wars. Their primary WWII function began with reconnaissance and underwater demolition of natural or man-made obstacles obstructing amphibious landings. They later were tasked to ensure recovery of space capsules and astronauts after splash down in the Mercury, Gemini and Apollo space flight programs. UDTs 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.