- He apparently died on British prison ship during the war. There are five William McLellans listed in Massachusetts Soldiers and Sailors in the War of the Revolution in vol. 10 (pages 543-44). I would guess, if family history is correct, that he is this one:
Mclellan, William.1st Lieutenant, sloop "Retrieve" (privateer); petition dated Watertown, Aug. 29, 1776, signed by John Fox, in behalf of himself and others, of Falmouth, Casco Bay, asking that Joshua Stone be commissioned as commander [p.544] of said vessel; ordered in Council Aug. 29, 1776, that a commission be issued; also, list of prisoners on board the cartel "Hostage" to be exchanged for British prisoners, as returned by Thomas Stone, Commissary [year not given]; said McLellan, 1st Lieutenant, reported taken in the sloop "Retrieve" (privateer), of Casco Bay, by the British ship "Milford."
According to Miller, "He enlisted as a private in Capt. Reed's Company, Samuel Cobb's regiment, July 23, 1871, and was discharged Dec. 1, 1871. The company was raised for the defense of the sea coast of Eastern Masschusetts. Mr. McLellan died on board a prison ship in the Revolutionary War. He was the son of Capt. George McLellan, who married Mary Webster of Portland. Capt. McLellan was a shipmaster and was lost at sea with his son George. It is possible that John, Samuel, and William McLellan resided in Thomaston when they entered military service. Members of the McLellan family, howeer, resided in Cushing in the early history of the town."
I would guess that he was a privateer, which many New Englanders were during the Revolution. Privateers were employed by the Continental Congress to harry British shipping, and were quite successful. It was also a good way for New Englanders to get rich--they could keep the prizes they won. When privateers were captured, they were often held in prison ships; one of the notorious ones was the New Jersey, anchored off of New York. They were pretty squalid.