World War I transformed Uganda's military establishment. Its personnel grew from 1,058 to 8,190. Emergency legislation upgraded the Fourth Battalion to a regiment. Former Fourth Battalion personnel became part of the new Uganda Regiment, which eventually comprised six battalions. By the end of World War I, 16,000 Africans had served in the KAR and 178,000 had worked as laborers in the carrier corps, primarily in East Africa. The British government awarded decorations to 155 soldiers and mentioned the valor of many others in dispatches to the crown. Casualties in the Uganda Regiment included 225 deaths in battle or as the result of injuries in addition, 1,164 died from disease and at least 760 were wounded.

Ugandan soldiers saw little action during the interwar years but provided garrison duty on Uganda's northern frontier and at Meru and Lokitaung (both in Kenya). The colonial authorities reorganized the Uganda Regiment several times, however, and reduced its size to about 400. It included two rifle companies, a machine-gun platoon, a marching band, and a battalion headquarters staff at Bombo. In addition, 169 soldiers made up a reserve force.

In 1930 British officials on the Committee of Imperial Defence combined the remnants of the Uganda Regiment with the Third Battalion in Kenya to form the Northern Brigade, headquartered in Nairobi. In the late 1930s, as World War II approached, Uganda's governor, Sir Philip Mitchell, established the Seventh Territorial Battalion to bolster security in Uganda while other troops conducted operations in Kenya. Northern Ugandans dominated the army, although all major ethnic groups were eventually represented in the fighting forces.

Data as of December 1990