Duncan Sayre MacInnes CMG DSO CdeG was born in Hamilton, Ontario, a younger son of Honorable Senator Donald MacInnes and Mary (Robinson) MacInnes, daughter of Sir John B. and Mrs. Robinson. Duncan MacInnes graduated from Royal Military College (RMC), Kingston, Ontario in June 1951. In his final year he won the Governor General’s Gold Medal, the Sword of Honour and Spur.

In 1890 he enlisted in the Army and served with the Ashanti (West Africa) Expedition, with the rank of lieutenant, in the Royal Engineers. He had a great deal of staff service in the South African (Boer) War of 1899-1902. His resourcefulness and gallantry in defence of Kimberley, in the Orange Free State was reported on February 15, 1900, by his superior officer. For his services throughout the war, he was twice "Mentioned in Despatches" (1900 and 1902) and was awarded the Distinguished Service Order (DSO). Also he he received the Queen’s Medal with three clasps and the King’s Medal with two clasps.

From 1905 to 1907, he was Deputy Assistant Quartermaster General, Halifax, Nova Scotia for army forces in Canada. In September 1907 he was appointed Chief Staff Officer, Maritime Provinces Command. In March 1908 he was transferred to the War Office in England.

In 1913 he was a student at the Staff College, Camberley, Surrey, England. After graduating from Staff College, he was appointed a General Staff Officer in the Directorate of Military Training at the War Office. Subsequently he was appointed a member of the Directing Staff of the Staff College, an appointment he held until the outbreak of WW 1.

At the outbreak of WW 1, he went to the Western Front in France with the Royal Engineers. By the summer of 1915, the war on the Western Front had stalemated into one of attrition. After the second Battle of Ypres there followed sporadic frontal attacks on both sides without any result other than the slaughter of tens of thousands of men. Conditions were appalling. The troops lived in the squalor and dankness of the trenches, sometimes knee deep in water and mud.

Major McInnes was wounded during the Battle and Retreat from Mons, in November 1914. It was about this time that he returned to England and in 1915 served as an Assistant Director in the Department of Military Aeronautics at the War Office. From 1916 to 1917 he was Director of Aircraft Equipment. For his outstanding work in this role he was named a Companion of the Order of St. Michael and St. George (CMG). Full recognition was also given to his services when, at a dinner given to him on his departure, the Air Minister referred in the highest terms to the worth of his achievements in laying the foundation of aircraft production on a thoroughly sound basis. Despite an infinity of natural obstacles and personal hindrances, he succeeded in effecting remarkable increases in output, and, at the same time won the personal affection of all those who worked with him or under him.

In 1918, Brigadier General MacInnes returned to the Western Front in France with the Royal Engineers as Inspector of Mines. He was killed in an accidental mines explosion near General Headquarters in May 1918. He is buried in the military cemetery at Etaples, France. Russia appointed him to the Order of St. Stanislaus First Class. France named him an Officer of the Legion of Honour and also awarded him the Croix de Guerre.

In 1902, he married Millicent Thomas, daughter of Mr. and Mrs. F. Wolferstan Thomas of Montreal, Quebec. They had one daughter and one son, also named Duncan.