The development of machine gun doctrine from 1898 to the end of the First World War is an example of military innovation in action. This thesis explores that development focussing on the men who created it as innovators. There are several different theories of military innovation put forward by Rosen, Posen, Murray, Foley and Farrell, and this thesis will examine them with regard to the development of machine gun doctrine. There were four major innovators. An American, John Henry Parker honed his skills in the Spanish American War of 1898 and used this experience to develop machine gun doctrine for the US Army. He can be identified as the ‘father of machine gun doctrine’ as his ideas were adopted by Allied armies during the First World War. Parker’s work was taken up by the British officer R.V.K. Applin in 1910. Applin was active in the period before the war in trying to influence senior figures in the power of machine guns. He spent much of the war in India and America as a machine gun trainer. George M. Lindsay was the most influential British machine gun officer of the war. He was responsible for the establishment of the Machine Gun Corps in 1915 and through his work in the machine gun schools in Grantham and Camiers developed most of the machine gun doctrine for the British Army. The Frenchman, Raymond Brutinel, who fought for the Canadian Expeditionary Force, was the most influential machine gun officer in the Allied armies during the war. He was remarkable in that he had no major military experience at the outbreak of war. Yet he equipped and raised a motorised machine gun unit with his own money and turned it into the first mechanized ‘all arms unit’ which during the 100 Days Offensive made a significant contribution to overall victory. He was also responsible for developing the idea of barrage fire which played no small part in the victory of the C.E.F. at Vimy Ridge. This tactic was then disseminated to the rest of the British army and used effectively in the Battle of Messines by R.V.K. Applin. He was appointed a Brigadier General in 1918 and became the highest ranked machine gun officer of the Allied armies. This thesis highlights the complexities of innovation in a military setting that can occur at different levels across formations and institutions, and will act as a guide to future study in this area.