Mugford commanded the schooner Franklin in the Continental Navy, serving through 1775 in John Manley's squadron off Boston.
Franklin was attacked during the night of May 19, 1776 in the company of Lady Washington (a small privateer schooner with a crew of 7 commanded by Joseph Cunningham) by British boarders claiming to be friends from Boston; Captain Mugford was killed in action.
... was attacked by five boats, which were supposed to contain near or quite a hundred men; but after repeated efforts to board her they were beaten off by the intrepidity and exertions of the little company, who gloriously defended the Lady against the brutal ravishers of liberty.Mugford had captured a British ship and, having delivered her and her cargo to Boston, he enlisted the Lady Washington to ferry him back to his own ship, the Franklin.
Mugford warned them to keep their distance and fired his cannons loaded with musket balls when they ignored him.
According to a report in The Pennsylvania Evening Post, Mugford was killed by a musket ball rather than a lance.