Dagger formerly belonging to T E Lawrence, more widely known as Lawrence of Arabia.
Known as a ‘jambiya’, this example is steel and silver, and was famously presented to Lawrence by Sherif Nasir in 1917 after the victory of the Arabs at Aqaba on 6 Jul 1917 in modern-day Jordan, in which Lawrence had participated. 
Wearing a jambiya was customary for men at the time, and would have helped Lawrence further ingratiate himself with his Arab allies. It helped complete his transition from the khaki-clad British soldier, to the Arab leader.
Associated with the World War One, Arab Revolt (1916-1918).