The service records of around 110,000 Royal Marines have been made available at The National Archives’ website Documents Online www.nationalarchives.gov.uk/documentsonline. The records cover the period 1842-1936.
Linda and I took a look to see if we could find the service record of the man we think was her great-grandfather, William Freeth, as we hadn’t been able to trace it at The National Archives at Kew. No such luck! We had found him in one of the Royal Marines’ description books, so at least we do know he was in the Marines. I hope you have more success online than we did.