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Here are a few details I have found about the voyage of AMERICAN FARMER during which time your grandfather was aboard. I find a William H. McDavid in the crew listing, serving as first assistant engineer, confirming what you have stated. At the time he was age 33 with ten years of sea time behind him. He was described as 5'9" tall and 198 lbs., with a scar on his left thumb.
Along with most of the rest of the crew, he signed aboard AMERICAN FARMER on April 19, 1945, in Wilmington, NC. AMERICAN FARMER was constructed by the North Carolina Shipbuilding Company of Wilmington, being completed in April 1945, so this was her maiden voyage. She was a so-called class C2 cargo ship, 459 feet long, 63 feet wide, draft of 25 feet, powered by two turbine engines, speed of 15.5 knots. (See http://shipbuildinghistory.com/history/shipyards/4emergencylarge/wwtwo/northcarolina.htm and scroll to hull number 206. Also see http://drawings.usmaritimecommission.de/drawings_c2.htm for a side drawing of a typical ship; AMERICAN FARMER is specifically noted about 2/3 of the way down the page at design C2-S-AJ1.)
(Note that there were two other ships named AMERICAN FARMER. The first, built in 1920, was torpedoed and sunk in April 1941 under a different name and under the Belgian flag. Another ship named AMERICAN FARMER was constructed in 1942, turned over to the U.S. Navy and renamed. So by 1945 there was only one ship by that name.)
AMERICAN FARMER departed Wilmington, NC, on an unspecified date and proceeded to New York, arriving on an unspecified date, perhaps to load cargo. She left New York on May 14, 1945, and proceeded to Hampton Roads (i.e., Norfolk area), departing there on May 18 as part of convoy UGS-93, destination Oran, Algeria. (See http://www.convoyweb.org.uk/ugs/index.html and scroll to UGS.93.) The convoy reached Oran on June 4 but, reading between the lines, AMERICAN FARMER apparently continued eastward through the Mediterranean. With the European war over by that time she may have sailed independently, i.e., not in a convoy. She proceeded through the Suez Canal and reached Bombay, India. The original crew manifest contains stamps and other markings affixed by the U.S. Consulate, one of which is for Bombay and dated June 22. This may have been the date the ship either arrived in or departed Bombay, I don't know which.
Your information that one of your grandfather's letters, dated June 26, indicated there were in a small native town with multiple Catholic churches is interesting, as that would not seem to describe either India (primarily Hindu with a tiny Christian population), or any Arabian or North African country (primarily Islamic). Could it have been Ceylon (now Sri Lanka), which is primarily Buddhist but with a relatively small (primarily Catholic) population along the northwest coast? Jaffna is a sizable city in this area and has a number of outlying islands and towns.
AMERICAN FARMER returned to the Mediterranean, reaching Port Said, Egypt, from which she sailed on July 25 (per consulate markings), and returned to New York on August 7, 1945. It is likely she sailed independently on the westbound return voyage.
I hope this may be useful to you.
Ron Carlson, Webmaster
Armed Guard / Merchant Marine website