The rank, serial number, and the passes, imply that he was a Royal Marine. Serial numbers beginning PL or PLY were used by Marines belonging to the Plymouth Division - the Royal Marines were allocated to three divisions, Plymouth, Portsmouth and Chatham. These divisions, based at the ports for which they were named, were responsible for training and administration for the men allocated to them. Those men would also return to their division between service at sea or abroad. The Royal Navy also manned its ships from depots at these ports, with Plymouth marines serving aboard Plymouth ships and so on. Repulse and Revenge were both Plymouth ships, so it's not implausible that your Grandad served on both ships. Beyond that, it's hard to say what he would have been up to without a service record. The Royal Marines Museum has a good document on obtaining and interpreting a service record here, and I'd be happy to give you more help contextualising what you find.

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!