During World War II, There was an internal treaty between Nepal and Britain about the mobilization of Nepalese soldiers.

The Nepali units which took part were Sri Nath, Kalibox, Surya Dal, Naya Gorakh, Barda Bahadur, Kali Bahadur, Mahindra Dal, Second Rifle, Bhairung, Jabbar Jung, Shumsher Dal, Sher, Devi Dutta, Bhairab Nath, Jagannath and Purano Gorakh Battalions. Besides, there were many high ranking Nepalese in the joint Army HQ. Late Commander-in–Chief Kiran Shumsher Rana and ex-Commander-in-Chief and present Field Marshall Nir Shumsher Rana were liaison officers from the Royal Nepalese Army.

When Japan got involved in this war in December 1940, the British presence was threatened in the Indian subcontinent. Britain deployed its troops in India and on theBurma front. Nepalese battalions – Mahindra Dal, Sher, Kali Bahadur and Jagannath- were also deployed. These Nepalese battalions fought under the Allied Command. The Jagannath Battalion took part as engineers to construct tracks, bridges, water points etc.

Nepalese troops fought with distinction in the 14th Army under Slim and helped force the eventual Japanese retreat. Finally, following the atomic bomb attacks on Hiroshima and Nagasaki, Japan surrendered. Most Nepalese troops were withdrawn to Kathmandu in Oct 1945. A grand victory parade was held on 28 October 1945 where many Nepalese soldiers, officers and associated British officers were honored for their appreciable performances.