While I was down here in Melbourne I spent a few days looking through the files on the topic at the National Archives. They gave me a note from somweone else who is researching the Naval Beach Commandos.
During an amphibious operation, someone needs to take control of the beach. Marking the beach, liaising with the navy, saying who lands what and when so the beach doesn't get jammed up is a naval responsibility and during WWII, the RAN organised Beach Commandos to handle the job. They formed an integral part of two Army Beach Groups, which handled beach operations from the Army side. Formed in late 1943, they saw action on Borneo, in the operations at Tarakan, Labuan and Balikpapan in May, June and July 1945 - the last amphibious operations of the war.
Apparently, the researcher who sent me the note works for the Naval Historical Society and has been researching the Beach Commandos for them. How strange that two people should be researching something when nobody has been interested in it for over half a century!