John Girling Burton RN

I am researching my Grandparents military service. My paternal Grandfather John Girling Burton served in th Royal Navy having first signed up at the age of 15 in 1918. My father has mentioned him serving with Royal Navy Beach Commando alongside the Canadian Navy Commando at Juno however he has no records to support this, we have is his naval service record but this makes no mention RN Commando. Would this have been normal and been on a separate record ? I would appreciate any assistance you could provide to help with my research.

Kind Regards

Jon Burton