May 21, 1639Lord Deputy Thomas Wentworth Imposes the Black Oath of Loyalty to Charles I on All Ulster Scots Over the Age of 16
May 21, 1650James Graham, (Montrose), Scottish Royalist Commander, Executed by Cromwellian Government
May 21, 1745Count Daniel O'Connell, a Soldier in French and British Services, Is Born in Derrynane, Co. Kerry
May 21, 1916Clocks and Watches Go Forward One Hour as the Daylight Saving Act (Summer Time) Is Introduced