Re: LS&GC - split service
Royal Navy: An Other Rank who completes 15 years of reckonable service from the date of attestation or age 17½, whichever is later, and who holds all three good conduct badges, shall be eligible to receive the medal.
Army: A soldier who completes 15 years of reckonable service from the date of attestation or age 17½, whichever is later, shall be eligible to receive the medal.
As I understand it, he would have had to be discharged from the Navy and then re-enlist into the Army. The two periods of service would be independent of each other and not a continuance of service.