What was the operation in preparation for which the NCDUs were deployed in April 1944?

The correct response is Operation Overlord. This operation refers to the Allied invasion of Normandy during World War II, which began on June 6, 1944, commonly known as D-Day. The Naval Construction Battalions (NCDUs) were critical in preparing for this operation by clearing obstacles on the beaches and ensuring that landing forces could establish a foothold in Europe. The deployment of the NCDUs in April 1944 was a strategic move to facilitate the massive amphibious assault and to make sure that the necessary preparations were in place to support the main battle.

The other operations mentioned did not involve the deployment of NCDUs in April 1944. Operation Neptune was specifically the naval component of Operation Overlord, but it was not the operation for which NCDUs were initially deployed. Operation Torch was the Allied invasion of North Africa in 1942, which occurred well before the timeline in question. Similarly, Operation Market Garden, which took place in September 1944, did not involve the NCDUs in the same preparatory capacity as was needed for the D-Day landings. Thus, Operation Overlord is the operation related to the deployment of the NCDUs in April 1944.