Which unit provided hydrographic reconnaissance and underwater demolition of obstacles in WWII?

The Underwater Demolition Teams (UDTs) were specifically formed as a naval unit during World War II to conduct hydrographic reconnaissance and underwater demolition of obstacles. Their primary mission involved clearing paths for amphibious landings by removing underwater barriers like mines, barbed wire, and other obstacles. UDTs played a crucial role in several major operations, including the invasions of Normandy and the Pacific islands, where they gathered crucial intelligence about the beaches and the conditions while also ensuring safe passage for landing forces.

In contrast, while Non-Combat Demolition Units (NCDUs) also conducted demolition work, their focus was more on clearing specific landing sites rather than the broader hydrographic reconnaissance responsibilities that UDTs tackled. The Office of Strategic Services (OSS) and the Army Rangers had distinct roles, with the OSS engaged in intelligence and sabotage operations behind enemy lines, and Army Rangers primarily involved in direct combat and assaults, rather than specialized underwater operations.