Brigadier-General Duncan Sayre MacInnes CMG DSO (21 February 1860 – 23 May 1918) was a Canadian soldier and engineer who served in South Africa before, during and after the Second Boer War.

[4] His father was Senator Donald MacInnes from Hamilton, Ontario, and his mother was the fourth daughter of Sir John Robinson, 1st Baronet, of Toronto.

He served as deputy assistant quartermaster general at Halifax, Nova Scotia in 1906, turning over the fortress and garrison to Canada.

He was in command of the 54th field company of Royal Engineers, part of the 7th Division, participated in the retreat from Mons, and in late November received a wound which permanently restricted the use of fingers on his right hand.

In 1916, he was appointed director of aircraft equipment, in charge of design, supply, and maintenance, and subsequently made a temporary brigadier-general.

Faced with extraordinary demands for more and better aircraft, an overwhelmed system of procurement, and malicious attacks from superiors, an overworked MacInnes suffered a breakdown in the fall of 1916 and he left the directorate in early 1917.

MacInnes was accidentally killed while visiting the front on 23 May 1918, possibly as a result of his work with mines, and he was buried at Étaples, France on 25 May 1918.