Lieutenant-General William Godfrey Dunham Massy CB (24 November 1838 – 20 September 1906) was a senior officer in the British Army.

He was born the eldest son of Major Henry William Massy (1816–1895) of Grantstown and Gonmaine, County Tipperary, Ireland and educated at Trinity College, Dublin, where he graduated B.A.

During the Second Anglo-Afghan War of 1879–80 he commanded a cavalry brigade and took a prominent part in the Battle of Charasiab on 6 October 1879, capturing 75 pieces of Afghan artillery.

During the subsequent operations in the Charde Valley, Massy was despatched in pursuit of the enemy but failed to cut off their retreat.

In the actions round Kabul in December, he was ordered to start from Sherpur with his cavalry and meet up with General Macpherson's brigade.

Advancing too far, he was cut off by 10,000 Afghans at Killa Kazi, and after an unsuccessful charge and the abandonment of guns he had to be rescued by the main force.