In the spring of 1942, the dock was used for training the commandos who were to take part in the raid on the French port of St. Nazaire. The King George V dock was very similar in design and construction to the Normandie dry dock at St. Nazaire, thus enabling the commandos to familiarise themselves with the construction of the dock. The men practised descending the stairs of the pumping chamber in the dark and setting explosives against the pump mechanism; they also practised climbing inside the hollow caisson to set explosives and setting charges against the gate winding machinery. In the raid itself, the obsolete destroyer HMS "Campbeltown" was rammed into the Normandie dock gates and exploded, while the commandos destroyed the dock machinery.