Hi Michael, there is a tree on Ancestry under the surname of Gibson with a photograph of your grandfather in his later years, no details of his MN career in her tree but she may be able to add further details regarding him, if you wish I could send her a message to contact you?
There is also a photograph of his wife Olga sitting with a newborn baby boy and another child around 4-5yrs beside her.
This might be him:
New York State, Passenger and Crew Lists, 1917-1966
Name: Henry Hawkins
Arrival Date: 12 Sep 1944
Arrival Place: New York, New York, USA
Ship: MAURETANIA
Port: New York
Rank: Rating, AB then listed under [ON]? R/JX 326322
Another family tree under the name of David Cadwalader Taylor has the same photograph and states Henry joined the Royal Navy 1943