Which operation is known as the first major combat deployment of UDTs?

The first major combat deployment of Underwater Demolition Teams (UDTs) occurred during Operation Flinder's Lane, which took place in the Pacific Theater during World War II. This operation involved reconnaissance and demolition missions aimed at preparing for amphibious assaults by clearing obstacles and scouting beach conditions.

UDTs were formed to handle specific tasks related to the preparation of beachheads, such as explosives removal and underwater reconnaissance, which were critical for the success of larger amphibious operations. Operation Flinder's Lane demonstrated the effectiveness and strategic importance of these specialized teams in an actual combat scenario, paving the way for their broader use in subsequent operations.

Other operations listed, such as Operation Overlord and Operation Torch, though significant in their own right, did not represent the UDTs' initial deployment for combat. Operation Neptune refers specifically to the naval component of Operation Overlord, which included landing forces on the beaches of Normandy, but UDTs had already been utilized in prior preparatory operations like Flinder's Lane.