Underwater Demolition Teams (UDT) were the precursor to the current United States Navy SEALs. The first group of volunteers selected from the Naval Construction Battalions (Seabees) in the spring of 1943. These volunteers were organized into special teams called "Navy Combat Demolition Units" (NCDUs). The units were tasked with reconnoitering and clearing beach obstacles for troops going ashore during amphibious landings, and evolved into Combat Swimmer Reconnaissance Units; this is a type of frogman operation.

The NCDUs distinguished themselves during World War II in both the Atlantic and Pacific theaters. In 1947, the Navy organized its first underwater offensive strike units. During the Korean Conflict, these Underwater Demolition Teams (UDTs) took part in the landing at Inchon as well as other missions including demolition raids on bridges and tunnels accessible from the water. They also conducted limited minesweeping operations in harbors and rivers.

During the 1960s, each branch of the armed forces formed its own counterinsurgency force. The Navy utilized UDT personnel to form separate units called SEAL teams. Concurrently, Naval Operations Support Groups were formed to aid UDTs, SEALs, and two other unique units —Boat Support and Beach Jumpers— in administration, planning, research, and development. During the Vietnam War, UDTs performed reconnaissance missions.

In 1967, the Naval Operations Support Groups were renamed "Naval Special Warfare Groups" (NSWGs) as involvement increased in special operations. In 1983, existing UDTs were re-designated as "SEAL teams" or "SEAL Delivery Vehicle Teams" and the requirement for hydrographic reconnaissance and underwater demolition became "SEAL missions".

For those who served in an Underwater Demolition Team, the U.S. Navy authorized a military badge known as the Underwater Demolition Badge. The badge was phased out and eventually replaced by the Special Warfare Badge. In the modern age, the Underwater Demolition Badge is considered obsolete.