Military records of veterans who served after 1900 are available through the National Archives, specifically from:
National Personnel Records Center
Military Personnel Records
9700 Page Avenue
St. Louis, MO 63132-5100
Information on obtaining a veteran's military record can be found on the following National Archive web pages:
Note, however, that it is much easier for a veteran's next-of-kin (spouse, parent, brother, sister, child) to obtain the veteran's complete records than for someone who is not next-of-kin. Since you are not next-of-kin, someone who is next-of-kin will have to obtain the records for you, or you can obtain the records yourself with the written permission of the next-of-kin, or you will have to be satisfied with a more limited amount of information (see http://www.archives.gov/st-louis/military-personnel/foia-info.html#mprfoia). However you may find that even the limited amount of information will be adequate for your purposes. Since the records of a veteran's "Assignments and Geographical Locations" are available to the general public, the ships on which your uncle served should be available in service records that you can obtain.
Assuming you obtain your uncle's service records and assuming they list all the ships on which he served, you can identify the ports to which he sailed by returning to the National Archives. The Archives has custody of a wide range of records relating to warships, merchant ships on which Armed Guard units served, and other Navy units for the period from World War II through Vietnam, with a heavy concentration in World War II records. You would probably be particularly interested in Armed Guard logbooks and reports, action reports, vessel movement report cards, and records of individual convoys.
To learn more about the scope of these materials and to request records for a given ship, write to the following address:
Modern Military Records Unit (NWCTM)
National Archives and Records Administration
8601 Adelphi Road
College Park, MD 20740-6001
In your letter, include the names of the ships, the date/time period of interest; your full name, address, and telephone number; and as much other detail as possible about the information you would like to obtain. Due to the volume of requests received and the time needed to identify all appropriate records, Archives staff requests that you limit your request to five items per each letter. Allow approximately 10 – 12 weeks from the initial inquiry to receipt of the records.
A charge will be imposed for reproduction/mailing of the records, however do not send any cash/check/charge card information with your initial inquiry. Archives staff will review your request and mail to you an estimate of the cost and payment information. Follow the directions contained in that letter to order the desired records.
Additionally, the website Ancestry.com, which is more commonly used for genealogical research purposes, provides access to databases of passengers arrivals in various U.S. ports of entry between 1820 and 1957. Included in this database are the names of Armed Guard and merchant marine crew members whose ships arrived in those ports during World War II. Making a search at Ancestry.com for your uncle's name, I discovered a record of his arrival in the port of New York on August 30, 1942, aboard the SS THOMAS RUFFIN, which arrived in New York from Liverpool, England. He was identified as a member of the 16-man Armed Guard crew on that ship; the only other useful identifying information is that he was 30 years old, 5'5" tall and 130 pounds.
There is a record at http://www.warsailors.com/convoys/sc91.html of the THOMAS RUFFIN sailing in convoy SC-91 from Sydney, Nova Scotia, to Liverpool, between July 10 and July 24, 1942. It may be RUFFIN's return voyage from Liverpool to New York that is recorded in Ancestry.com.
(Later the THOMAS RUFFIN was torpedoed, but did not sink, in the Gulf of Mexico on March 9, 1943, presumably after your uncle left the ship. Four crewmen and two Armed Guard were lost. A picture of the THOMAS RUFFIN is available at http://www.uboat.net/allies/merchants/ship.html?shipID=2751)
Also at Ancestry.com is the record of a man named Leifier Benedicktson, who may be your uncle, appearing on the muster rolls of the aircraft carrier USS ESSEX (CV-9) in April 1943. (ESSEX was newly commissioned and undergoing sea trials at this time; she made her first voyage, from Norfolk to the Pacific, beginning in May 1943.) His service numbers was 638-31-64 and he was a seaman first class. Note that his service number and rating were not included in the record of his 1942 arrival with the THOMAS RUFFIN.
I hope this information is useful.
Ron Carlson, Webmaster
Armed Guard website www.armed-guard.com