Have you tried ordering his naval service records?
I found him listed here:http://research.archives.gov/search
Yamrovich John Lewis
[Service Number] 002433893
[Date of Enlistment] 03/03/1930
National Archives Identifier: 4467451
Local Identifier: NV14591043
Creator(s): Department of Defense. Department of the Navy. Bureau of Naval Personnel. (1991 - ca. 1995)
siWWI Navy Enlisted Block Yamrovich
According to the site, you can get the records from:
NARA's National Personnel Records Center
(Archival Operations Branch) (NRPAO),
9700 Page Avenue
St. Louis, MO 63132-5100
More re: ordering the records:http://www.archives.gov/veterans/military-service-records/
The instructions are very confusing BUT I think that his records are probably archival and thus open to the public.
Also, the website lists all this info that is needed (which you don't have) BUT the actual form reads "Furnish as much as possible." I would think that the above service number will be sufficient.