Glyndŵr entered the English king's military service in 1384 when he undertook garrison duty under the renowned Welshman Sir Gregory Sais, or Sir Degory Sais, on the English–Scottish border at Berwick-upon-Tweed. In August 1385, he served King Richard II under the command of John of Gaunt, again in Scotland. On 3 September 1386, he was called to give evidence in the "Scrope v Grosvenor" trial at Chester. In March 1387, Owain was in southeast England under Richard FitzAlan, 4th Earl of Arundel, in the English Channel at the defeat of a Franco-Spanish-Flemish fleet off the coast of Kent. Upon the death in late 1387 of his father-in-law, Sir David Hanmer, knighted earlier that same year by Richard II, Glyndŵr returned to Wales as executor of his estate. He possibly served as a squire to Henry Bolingbroke (later Henry IV of England), son of John of Gaunt, at the short, sharp Battle of Radcot Bridge in December 1387. He had gained three years' concentrated military experience in different theatres and seen at first hand some key events and people.