In 1898, as negotiations over the voting rights of British settlers in the Boer territories of Transvaal and Orange Free State failed and the Boer War broke out, he needed little encouragement when in December Basil Williams, a colleague at Westminster and already a member of the volunteer Honourable Artillery Company, suggested that they should enlist together. Childers joined the City Imperial Volunteers, something of an "ad hoc" force comprising soldiers from different territorial regiments, but funded by City institutions and provided with the most modern equipment. He was an artilleryman classed as a "spare driver", caring for a pair of horses and riding them in the ammunition supply train.