This operation is linked to Operation Roast.
Battle of the Argenta Gap, Lake Comacchio, Italy, launched on the 1st April 1945 involving the whole of 2 Commando Brigade. Operation Roast was an attack across Lake Comacchio to capture the spit of land between Lake Comacchio and the Adriatic Sea, from the River Reno to the Valetta canal, a distance of about 7 miles. It was essentially a plan to draw German reserve forces away from the main offensive to be launched across to the East. This was followed by Operation Impact Plain on the 10/11th April at the southern tip of Lake Comacchio, and Operation Impact Royal 13-16 April at Fossa Marina, East of Argenta.
A good description of the action during Impact Royal can be found in the award citation for Lance Sergeant L.W. Hopkins DCM [view....].