Masefield was a 23rd century Human male. By the late 2250s, Masefield was serving in Starfleet as a lieutenant assigned to the USS Constitution. Masefield was trained to assume a number of roles on a starship's bridge, including navigator and tactical officer. In 2257, Masefield worked at the navigation console whilst Gary Mitchell was off shift. He was later relieved by Mitchell during the battle with the N'shaii mothership, but remained on the bridge, taking the weapons console.