The original concept for the Centaurs of the Royal Marine Armoured Support Group was to provide fire support for the Marine Commandos on D-Day. They were to be hard mounted into Tank Landing Craft that would stay just off the beach and fire on pillboxes and other defensive positions. Once the Beachhead was established they would be beached a continue to provide fire support from the shoreline. The engines were to be removed and the additional space used to store additional ammunition.
As the Marines are controlled by the Navy, they were to provide fire support according to Naval fire principles not Artillery principles. They had Naval sights installed (the armoured box on the turret) and the azimuth markings painted on the turret. The commander was the stand on the engine deck and direct fire by ordering the turret traversed until the azimuth matched the target.
During an exercise it was suggested that they would be of more use if they were to land and advance with Marines. With that, the engines were re-installed and Army drivers transferred to the Marines. They received no technical support and were to remain ashore for less than a week and within 1 mile of the beach. Fifteen days later and a good 10 miles inland, they were handed over to the Royal Artillery when the Marines were withdrawn from Normandy.
An ad hoc battery was formed that continued to support the advance thru July. In early August it was disbanded due to demands for replacements in other RA units. The Canadian Artillery took over the Centaurs and provided close support to 6 Airborne Division until the end of August when the Airborne was withdrawn from the front. The remaining vehicles were handed over to the French.
Cheers,
Rich