Whether or not he ever served Spain, in 1572 Williams took part in a raid during the siege of Ter Goes, South Beveland, an outpost of the main Spanish base at Middelburg which was also under siege. The garrison was far larger than they had expected and the attack failed, with many of the raiding party being killed. Williams and Rowland Yorke escaped by crawling out through ditches on their stomachs. In 1577 he joined John Norreys' expedition of English volunteers to the Low Countries, serving as Norreys' military adviser.