He was the eldest son of Captain Vincent Jesson Applin, Military Train, of "Exeview", Alphington, near Exeter. Following education at Sherborne School, he initially sought employment as a stage actor. However, in December 1889 he became a cadet with the BritishNorth Borneo Company. He continued to serve in the company's administration of the protectorate, becoming successively a police magistrate and justice of the peace for Labuan and a District Officer. He was involved in the suppression of the Mat Salleh Rebellion from 1895–1897 and was awarded The British North Borneo Company's Medal and clasp. After eight years service Applin had reached the rank of Captain Superintendent in the British North Borneo Armed Constabulary, but was forced to resign due to ill health and returned to England. He wrote an account of his years in North Borneo entitled Across the Seven Seas.
Military service
Second Boer War
In November 1898 Applin obtained a commission as a captain in the 6th Battalion, Lancashire Fusiliers. With the outbreak of the Second Anglo-Boer War in 1899 the battalion was mobilised and sailed to South Africa. He was appointed District Commissioner at Bloemfontein in June 1900 and acting Provost-Marshal for the Orange River in October of the same year. He subsequently saw active service in the Cape Colony, the Orange Free State and the Transvaal, and was twice mentioned in despatches. In April 1902 he was granted the local rank of Captain in the Army whilst serving with a provisional battalion, and the following August he transferred to the Royal Garrison Regiment. For his service in the war, he was made a Companion of the Distinguished Service Order in the October 1902 South African Honours list. The following year he was appointed Brigade Major of Royal Artillery at Gibraltar.
Development of machine gun tactics
In July 1905 he transferred to a regular line regiment, the 14th Hussars. In August of the same year he was seconded to the General Staff and was appointed Deputy Assistant Adjutant General for Musketry in Malta. In December 1906 Applin returned to his regiment, and in June 1911 promoted to major. During this period he was involved in developing tactics for the use of the machine gun, and in 1909 published one of the first books on the subject, Machine Gun Tactics.
During the First World War Applin became an instructor in the use of the machine gun, and was attached to the Machine Gun Corps Training Centre in July 1916. In November 1916 he was appointed temporary lieutenant-colonel, and commanded the machine guns of the II ANZAC Corps at the battles of Messines and Passchendaele. With the entry of the United States into the war, Applin was part of a British mission to the country, and gave lectures on machine gun tactics. He remained with the MGC until July 1919. In January 1919 Applin was given the brevet rank of lieutenant-colonel and in February was made commanding officer of the 14th Hussars. He retired from the army in January 1921.
Politics
With the ending of his military career, Applin entered politics. After making two unsuccessful attempts to enter parliament with minor parties, he became the Conservative MP for Enfield.
Applin was originally a member of the National Party, a xenophobic party that broke away from the Conservatives in 1917. He stood at the parliamentary by-election at Dartford in April 1920. The party came in a poor fourth place, with Applin losing his deposit. The intervention of the National Party and an Independent candidate split the Conservative vote and allowed John Edmund Mills of the Labour Party to secure an unexpected victory. The National Party was disbanded a year later.
