Until the independence of India, the "Indian Army" was a British-commanded force defined as "the force recruited locally and permanently based in India, together with its expatriate British officers, the "British Army in India" referred to British Army units posted to India for a tour of duty. The "Army of India" meant the combined Indian Army and the British Army in India.
The British Indian Army was a critical force for maintaining the primacy of the British Empire, both in India and throughout the world. Besides maintaining the internal security of the British Raj, the Army fought in many other theatres: the Anglo-Burmese Wars; the First and Second Anglo-Sikh wars the First, Second, and Third Anglo-Afghan wars the First and Second opium wars, and the Boxer Rebellion in China and in Abyssinia.
In the 20th century, the British Indian Army was a crucial adjunct to British forces in both world wars. 1.3 million Indian soldiers served in World War I (1914-1918) with the Allies, in which 74,187 Indian troops were killed or missing in action.In 1915 there was a mutiny by Indian soldiers in Singapore. The United Kingdom made promises of self-governance to the Indian National Congress in return for its support but reneged on them after the war, following which the Indian Independence movement gained strength.
In World War II Indian soldiers fought alongside the Allies. In 1939, British officials had no plan for expansion and training of Indian forces, which comprised about 130,000 men (in addition there were 44,000 men in British units in India in 1939), whose mission was internal security and defence against a possible Soviet threat through Afghanistan. As the war progressed, the size and role of the Indian Army expanded dramatically, and troops were sent to battlefronts as soon as possible. The most serious problem was the lack of equipment.[25] Indian units served in Burma, wherein 1944-45, five Indian divisions were engaged along with one British and three African divisions. Even larger numbers operated in the Middle East. Some 87,000 Indian soldiers died in the war. By the end of the war, it had become the largest volunteer army in history, rising to over 2.5 million men in August 1945.
Upon the Partition of India and Indian independence in 1947, four of the ten Gurkha regiments were transferred to the British Army. The rest of the British Indian Army was divided between the newly created nations of India and Pakistan. The Punjab Boundary Force, which had been formed to help police Punjab during the partition period, was disbanded.[30] Headquarters Delhi and the East Punjab Command were formed to administer the area.
The departure of virtually all senior British officers following independence, and their replacement by Indian officers, meant many of the latter held acting ranks several ranks above their substantive ones. For instance, S. M. Shrinagesh, the ground-forces commander of Indian forces during the first Indo-Pak War of 1947-49 (and the future third COAS), was first an acting major-general and then an acting lieutenant-general during the conflict while holding the substantive rank of major, and only received a substantive promotion to lieutenant-colonel in August 1949.[31] Gopal Gurunath Bewoor, the future ninth COAS, was an acting colonel at his promotion to substantive major from substantive captain in 1949, while future Lieutenant General K. P. Candeth was an acting brigadier (substantive captain) at the same time.In April 1948, the former Viceroy's Commissioned Officers (VCO) were re-designated Junior Commissioned Officers, while the former King's Commissioned Indian Officers (KCIO) and Indian Commissioned Officers (ICO), along with the former Indian Other Ranks (IOR), were respectively re-designated as Officers and Other Ranks.
Army Day is celebrated on 15 January every year in India, in recognition of Lieutenant General K. M. Cariappa's taking over as the first commander-in-chief of the Indian Army from General Sir Francis Butcher, the last British commander-in-chief of India, on 15 January 1949. With effect from 26 January 1950, the date India became a republic, all active-duty Indian Army officers formerly holding the King's Commission were recommissioned and confirmed in their substantive ranks.