 His first main encounter was when he led an army of about 3,000 in the Battle of Glenmalure, County Wicklow in August, where his army was routed by Fiach McHugh O' Byrne, with casualties of 800.Later in the same year, he led a force of 800 to "Ard na Caithne" (Smerwick) in County Kerry where he massacred 600 Irish, Italian and Spanish troops who surrendered, a notorious incident known as the Siege of Smerwick.According to some versions of this event, Lord Grey de Wilton promised the garrison their lives in return for their surrender, a promise which he broke – this resulted in the Irish proverb 'Grey's faith'.