
During the Second World War (1939–1945), India was controlled by the United Kingdom, with the British holding territories in India that included over six hundred autonomous Princely States. British India officially declared war on Nazi Germany in September 1939. The British Raj, as part of the Allied Nations, sent over two and a half million soldiers to fight under British command against the Axis powers. India also provided the base for American operations in support of China in the China Burma India Theater.

The Japanese occupation of the Andaman Islands occurred in 1942 during World War II. The Andaman and Nicobar Islands, are a group of islands situated in the Bay of Bengal at about 1,250 km (780 mi) from Kolkata, 1,200 km (750 mi) from Chennai and 190 km (120 mi) from Cape Nargis in Burma. Until 1938 the British government used them as a penal colony for Indian and African political prisoners, who were mainly put in the notorious Cellular Jail in Port Blair, the biggest town (port) on the islands. Today they form a Union Territory of India.

The Anglo-Iraqi War was a British-led Allied military campaign during the Second World War against the Kingdom of Iraq under Rashid Ali, who had seized power in the 1941 Iraqi coup d'état, with assistance from Germany and Italy. The campaign resulted in the downfall of Ali's government, the re-occupation of Iraq by the British, and the return to power of the Regent of Iraq, Prince 'Abd al-Ilah, a British ally.

The Arakan Campaign of 1942–43 was the first tentative Allied attack into Burma, following the Japanese conquest of Burma earlier in 1942, during the Second World War. The British Army and British Indian Army were not ready for offensive actions in the difficult terrain they encountered, nor had the civil government, industry and transport infrastructure of Eastern India been organised to support the Army on the frontier with Burma. Japanese defenders occupying well-prepared positions repeatedly repulsed the British and Indian forces, who were then forced to retreat when the Japanese received reinforcements and counter-attacked.

Armoured Carrier, Wheeled, Indian Pattern (ACV-IP), known also as Indian Pattern Carrier or other similar names, was an armoured car produced in India during the Second World War. It was typically armed with a Bren light machine gun. Those produced by Tata Locomotives were called "Tatanagars" after the location of the works. 4,655 were produced, used by Indian units in the Far East and Mediterranean and Middle East Theatre, typically in divisional reconnaissance regiments.

The Provisional Government of Free India or, more simply, Azad Hind, was an Indian Provisional government established in Japanese occupied Singapore during World War II. It was created in October 1943 and supported by – as well as largely dependent on – the Empire of Japan.

The British Indian Army was the main military of the British Indian Empire before its decommissioning in 1947. It was responsible for the defence of both the British Indian Empire and the princely states, which could also have their own armies. The Indian Army was an important part of the British Empire's forces, both in India and abroad, particularly during the First World War and the Second World War.

Merchant seamen crewed the ships of the British Merchant Navy which kept the United Kingdom supplied with raw materials, arms, ammunition, fuel, food and all of the necessities of a nation at war throughout World War II — literally enabling the country to defend itself. In doing this, they sustained a considerably greater casualty rate than almost every other branch of the armed services and suffered great hardship. Seamen were aged from fourteen through to their late seventies.

The Burma campaign in the South-East Asian Theatre of World War II took place over four years from 1942 to 1945. During the first year of the campaign, the Imperial Japanese Army with aid from Burmese insurgents had driven British forces and Chinese forces out of Burma, and occupied most of the country. From May to December 1942, most active campaigning ceased as the monsoon rains made tactical movement almost impossible in the forested and mountainous border between India and Burma, and both the Allies and Japanese faced severe logistical constraints.

The fighting in the Burma campaign in 1944 was among the most severe in the South-East Asian Theatre of World War II. It took place along the borders between Burma and India, and Burma and China, and involved the British Commonwealth, Chinese and United States forces, against the forces of Imperial Japan and the Indian National Army. British Commonwealth land forces were drawn primarily from the United Kingdom, British India and Africa.

The Burma campaign was a series of battles fought in the British colony of Burma. It was part of the South-East Asian theatre of World War II and primarily involved forces of the Allies; the British Empire and the Republic of China, with support from the United States. They faced against the invading forces of Imperial Japan, who were supported by the Thai Phayap Army, as well as two collaborationist independence movements and armies, the first being the Burma Independence Army, which spearheaded the initial attacks against the country. Puppet states were established in the conquered areas and territories were annexed, while the international Allied force in British India launched several failed offensives. During the later 1944 offensive into India and subsequent Allied recapture of Burma the Indian National Army, led by revolutionary Subhas C. Bose and his "Free India", were also fighting together with Japan. British Empire forces peaked at around 1,000,000 land and air forces, and were drawn primarily from British India, with British Army forces, 100,000 East and West African colonial troops, and smaller numbers of land and air forces from several other Dominions and Colonies.

The Burma campaign in the South-East Asian Theatre of World War II was fought primarily by British Commonwealth, Chinese and United States forces against the forces of Imperial Japan, who were assisted to some degree by Thailand, the Burmese National Army and the Indian National Army. The British Commonwealth land forces were drawn primarily from the United Kingdom, British India and Africa.

The Japanese invasion of Burma was the opening phase of the Burma campaign in the South-East Asian theatre of World War II, which took place over four years from 1942 to 1945. During the first year of the campaign, the Japanese Army drove British Empire and Chinese forces out of Burma, then began the Japanese occupation of Burma and formed a nominally independent Burmese administrative government.

China Burma India Theater (CBI) was the United States military designation during World War II for the China and Southeast Asian or India–Burma (IBT) theaters. Operational command of Allied forces in the CBI was officially the responsibility of the Supreme Commanders for South East Asia or China. However, US forces in practice were usually overseen by General Joseph Stilwell, the Deputy Allied Commander in China; the term "CBI" was significant in logistical, material and personnel matters; it was and is commonly used within the US for these theaters.

The Battle of Christmas Island was a small engagement which began on 31 March 1942, during World War II. Assisted by a mutiny by soldiers of the British Indian Army against their British officers, Imperial Japanese Army troops were able to occupy Christmas Island without any land-based resistance. The United States Navy submarine Seawolf caused severe damage to the Imperial Japanese Navy cruiser Naka during the landings.

Operation Compass was the first large British military operation of the Western Desert Campaign (1940–1943) during the Second World War. British, Indian, Commonwealth and Allied forces attacked Italian forces of the 10th Army in western Egypt and Cyrenaica, the eastern province of Libya, from December 1940 to February 1941.
The East African campaign was fought in East Africa during the Second World War by Allies of World War II, mainly from the British Empire, against Italy and its colony of Italian East Africa, between June 1940 and November 1941. The British Middle East Command with troops from the United Kingdom, South Africa, British India, Uganda Protectorate, Kenya, Somaliland, West Africa, Northern and Southern Rhodesia, Sudan and Nyasaland participated in the campaign. These were joined by the Allied Force Publique of Belgian Congo, Imperial Ethiopian Arbegnoch and a small unit of Free French.

The Battle of Imphal took place in the region around the city of Imphal, the capital of the state of Manipur in northeast India from March until July 1944. Japanese armies attempted to destroy the Allied forces at Imphal and invade India, but were driven back into Burma with heavy losses. Together with the simultaneous Battle of Kohima on the road by which the encircled Allied forces at Imphal were relieved, the battle was the turning point of the Burma campaign, part of the South-East Asian Theatre of the Second World War. The Japanese defeat at Kohima and Imphal was the largest up until that time, with many of the Japanese deaths resulting from starvation, disease and exhaustion suffered during their retreat.

The Indian Air Force (IAF) is the air arm of the Indian Armed Forces. Its complement of personnel and aircraft assets ranks fourth amongst the air forces of the world. Its primary mission is to secure Indian airspace and to conduct aerial warfare during armed conflict. It was officially established on 8 October 1932 as an auxiliary air force of the British Empire which honoured India's aviation service during World War II with the prefix Royal. After India gained independence from United Kingdom in 1947, the name Royal Indian Air Force was kept and served in the name of Dominion of India. With the government's transition to a Republic in 1950, the prefix Royal was removed.

The British Indian Army during World War II began the war, in 1939, numbering just under 200,000 men. 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. Serving in divisions of infantry, armour and a fledgling airborne force, they fought on three continents in Africa, Europe and Asia.

The Anglo-Soviet invasion of Iran or Anglo-Soviet invasion of Persia was the joint invasion of the neutral Imperial State of Iran by the United Kingdom, Australia and the Soviet Union in August 1941. The invasion, codenamed Operation Countenance, was largely unopposed by the numerically and technologically outmatched Iranian forces. The multi-pronged coordinated invasion took place along Iran's borders with modern Iraq, Azerbaijan and Turkmenistan with fighting beginning on 25 August and ending on 31 August when the Iranian government formally agreed to surrender, having already agreed to a ceasefire on 30 August.

The Ledo Road was an overland connection between India and China, built during World War II to enable the Western Allies to deliver supplies to China and aid the war effort against Japan. After the Japanese cut off the Burma Road in 1942 an alternative was required, hence the construction of the Ledo road. It was renamed the Stilwell Road, after General Joseph Stilwell of the U.S. Army, in early 1945 at the suggestion of Chiang Kai-shek. It passes through the Burmese towns of Shingbwiyang, Myitkyina and Bhamo in Kachin state. Of the 1,726 kilometres (1,072 mi) long road, 1,033 kilometres (642 mi) are in Burma and 632 kilometres (393 mi) in China with the remainder in India. The road had the Ledo-Pangsau Pass-Tanai (Danai)-Myitkyina--Bhamo-Mansi-Namhkam-Kunming route.

Throughout World War II, both the Axis and Allied sides used propaganda to sway the opinions of Indian civilians and troops, while at the same time Indian nationalists applied propaganda both within and outside India to promote the cause of Indian independence.
The Rani Jhansi Regiment was the Women's Regiment of the Indian National Army, the armed force formed by Indian nationalists in 1942 in Southeast Asia with the aim of overthrowing the British Raj in colonial India, with Japanese assistance. It was one of the all-female combat regiments of the Second World War on all sides. Led by Captain Lakshmi Swaminathan, the unit was raised in July 1943 with volunteers from the expatriate Indian population in Southeast Asia. The unit was named after the Rani Jhansi Regiment after Lakshmibai, Rani of Jhansi.

The Royal Indian Navy (RIN) was the naval force of British India and the Dominion of India. Along with the Presidency armies, later the Indian Army, and from 1932 the Indian Air Force, it was one of the Armed Forces of British India.

The Battle of Singapore, also known as the Fall of Singapore, was fought in the South-East Asian theatre of World War II when the Empire of Japan captured the British stronghold of Singapore—nicknamed the "Gibraltar of the East". Singapore was the major British military base in South-East Asia and was the key to British imperial interwar defence planning for South-East Asia and the South-West Pacific. The fighting in Singapore lasted from 8 to 15 February 1942. The Japanese victory was decisive, resulting in the Japanese capture of Singapore and the largest British surrender in history.

The Syria–Lebanon campaign, also known as Operation Exporter, was the British invasion of Vichy French Syria and Lebanon from June–July 1941, during the Second World War. The French had ceded autonomy to Syria in September 1936, with the right to maintain armed forces and two airfields in the territory.

The Trans-Iranian Railway was a major railway building project started in Pahlavi Iran in 1927 and completed in 1938, under the direction of the then-Iranian monarch Reza Shah. It was entirely built with indigenous capital, and links the capital Tehran with Bandar Shahpur on the Persian Gulf in the south and Bandar Shah on the Caspian Sea in the north, via Ahvaz and Ghom. In 1961, under Reza Shah's son Mohammad Reza Pahlavi, it was extended from Bandar Shah to a new terminus in Gorgan. During the land reforms of Mohammad Reza Pahlavi in 1963, as part of the "White Revolution", the Trans-Iranian railway was extended to link Tehran to Mashhad, Tabriz and Isfahan.