If your grandfather was aboard the SS Wellart as a member of the merchant marine crew, you may be able to obtain his service records through the U.S. Coast Guard. Contact the Coast Guard's National Maritime Center, which maintains merchant marine personnel records, at:
U.S. Coast Guard National Maritime Center
Mariner Information (NMC-4)
100 Forbes Drive
Martinsburg, WV 25404
Telephone: (304) 433-3400
You may also wish to post a message on the "Shipmate Search" page at website "American Merchant Marine at War" at http://usmm.org/shipmate_search.html. Other parts of the same website may be of interest to you: see http://usmm.org
If your grandfather was a member of the U.S. Navy Armed Guard crew on the Wellhart, you may be able to obtain his service records from the National Archives via the National Personnel Records Center, Military Personnel Records, 9700 Page Avenue, St. Louis, MO 63132-5100. See http://www.archives.gov/veterans/
(I would guess it is more likely that your grandfather was a merchant mariner rather than an Armed Guard, based on the dates you have. By 1942 he was probably in his 40s which would have been old for an Armed Guard but well within reason for a merchant sailor.)
A Google search for "ss wellhart" turned up several interesting hits, including the story of how the Wellhart helped fight a fire on a torpedoed ship off the coast of New Jersey in January 1942; see http://www.randomhouse.com/catalog/display.pperl?isbn=9781400063185&view=excerpt
There is a brief description of the Wellhart on this page: http://www.hhpl.on.ca/GreatLakes/rename/details.asp?ID=1678
The Armed Guard website has a record of one other person who was a member of the merchant marine crew of the SS Wellhart at the same time as your grandfather, a Samuel A. Fore who served on the Wellhart from Feb 1942 through May 6, 1942. (The latter date is the same date you have for your grandfather. The date probably refers to the end of a voyage for the ship at which time the crew would have been paid off and departed.) See http://www.armed-guard.com/ffff.html. I do not know if Samuel A. Fore is still living and, if so, how to reach him. The Social Security Death Index (see below) shows a Samuel A. Fore who died in 2002.
You may wish to search the Social Security Death Index; see http://ssdi.rootsweb.com. A search for "John Dwyer" resulted in 653 hits of deceased men of that name (or that name plus a middle name or initial). A search for "John E Dwyer" produced 23 hits, several of whom either received their Social Security number while living in Massachusetts or were living in Massachusetts at the time of their death. If you know the exact or approximate date of your grandfather's birth or his Social Security number you may be able to identify possible matches from the 653 hits or the 23 hits I found. A search for "John Edward Dwyer" did not produce any hits.
A copy of your mother's birth certificate may have information on her father, including his birth date and birth location. A copy of their marriage certificate might have the same information.
Ron Carlson, Webmaster
Armed Guard website