Interesting! But surely the two Peters were related, with Peter snr recorded as born Port St Mary? Relative of father James?

Odd that these records were not on FMP, but FamilySearch has:
Peter Mylchreest
United Kingdom, Merchant Navy Seamen Records, 1835-1941
military_service United Kingdom
birth: 1874 Isle of Man

Name Peter Mylchreest
Event TypeMilitary Service
Event Year Range1918-1921
Event Place United Kingdom
Birthplace Isle of Man
Birth Year1874

Peter Ronald Mylchreest
United Kingdom, Merchant Navy Seamen Records, 1835-1941
military_service United Kingdom
birth: 1905 Isle of Man

Name Peter Ronald Mylchreest
Event Type Military Service
Event Year Range1918-1921
Event Place United Kingdom
Birthplace Isle of Man
Birth Year 1905

Sue