As a piper aboard HMS Rodney, he would likely have been in the Marines anyway - the Marines provided ships' bands. It was also unlikely that he would have gone to the SAS, which drew mainly from Army units, rather than the Marines. However, he might have been a member of the SBS or the Marine Commandos. Identifying a ship by the number of survivors is difficult. The most famous ship to sink with just three survivors was the battlecruiser Hood, but James Howarth was not one of the survivors, nor was he one of those who died aboard her. The Royal Marine Museum has a number of good guides to locating and understanding a relative's service record here.

Hello there! As your question is related to looking for identification/information regarding military personnel, our Guide on Military Identification may be of use to you. It provides a number of different resources, including how to request service records from a number of national agencies around the world, as well as graphical aids to assist in deciphering rank, unit, and other forms of badges or insignia. While the users here may still be able to lend you more assistance, hopefully this will provide a good place to start!