Dear Mrs. Callahan,
Your best bet is to obtain a complete copy of your husband's official military service record. This will give you information on his entire military service, including the ships to which he was assigned.
To obtain a copy of your husband's military service record, see this page from the Armed Guard / Merchant Marine website: http://armed-guard.com/searchmil.html, in particular section II.A.1. - Records of Individuals - U.S. Military. You will have to contact the National Personnel Records Center, a records facility operated by the U.S. National Archives in St. Louis, MO. Provide as much identifying information as you have. There may be a charge for research time, photocopying and mailing, but the Records Center staff will provide an estimate on the cost before beginning work.
Ron Carlson, Webmaster
Armed Guard / Merchant Marine website