Which type of training did the NCDU provide personnel for during World War II?

The Naval Combat Demolition Units (NCDU) were primarily formed to support amphibious landings during World War II, particularly in European theaters. Their training focused on demolishing beach obstacles, clearing paths for landing forces, and conducting reconnaissance of landing sites. The NCDU played a critical role in operations such as the Normandy landings, where they were essential in ensuring that the assault forces could land successfully without being impeded by obstacles. This specialized training in explosive ordnance disposal and beach reconnaissance clearly highlights the significance of their operations in the European theater, making this the correct choice.

The other options do not accurately reflect the primary focus of NCDU training. While amphibious vehicle operations were part of broader military strategy, they were not the core of NCDU training. Trench warfare tactics were more relevant to World War I and are not associated with the NCDU's mission. Naval aviation support, although important during the war, was outside the scope of specialized NCDU functions, which centered around demolition and beach operations.