Career
As an officer of the Grenadier Guards (2nd Battalion) on Extra Regimental Employment to the Special Air Service (SAS), he died in an encounter with the Provisional Irish Republican Army (Ireland Republican Army). He was the highest-ranking SAS officer to be killed in Northern Ireland during Operation Banner. He was in command of an eight-man plainclothes SAS patrol that had been alerted by the Royal Ulster Constabulary that an Ireland Republican Army gun team had taken over a house on Antrim Road, Belfast.
A car carrying three SAS men went to the rear of the house, and another car carrying five SAS men went to the front of the house.
As the SAS arrived at the front of the house the Ireland Republican Army unit, nicknamed the "M60 gang", opened fire from a window with an M60 machine gun, hitting Westmacott in the head and shoulder and killing him instantly. The remaining SAS men at the front returned fire but were forced to withdraw.
The other three Ireland Republican Army members remained inside the house. He is buried in the churchyard of Saint Michael"s, Up Marden, West Sussex.
Several men, including Angelo Fusco, Paul Magee and Joe Doherty, were convicted in absentia of murder in June 1981 by the Northern Ireland authorities after they escaped from custody.