The context

On 7 December 1941, the Japanese attacked the US naval base at Pearl Harbour and later declared war on Britain and the United States.

In the days and weeks that followed, the Japanese invaded European colonies across East Asia, including the British territories of Hong Kong, Malaya, Singapore and Burma. They hoped to create a fortified perimeter around a self-sufficient Japan, which could be defended until the Allies tired of war.

The British had long thought a Japanese land invasion of Burma unlikely, so its defences had been neglected. When the attack began in January 1942, the British position quickly deteriorated. By March, the capital Rangoon and its vital port had been lost.

As the Japanese pushed northwards, the surviving Allied troops carried out a five-month fighting retreat to India across 1,000 miles (1,600km) of difficult terrain.