 In 1908, he joined the newly formed Territorial Force, Monmouthshire Regiment.By 1911 he was promoted to the rank of major, and with the outbreak of the First World War, he was posted to France with the rank of Lieutenant Colonel, commanding the 2nd Battalion of the Monmouthshire Regiment.Jenkins married Helena Leigh (née Roose) (birth registered during July→September 1879 in Wrexham district - death registered during October→December 1967 (aged 88) in Bournemouth district), sister of Wales association football international Leigh Richmond Roose, during July→September 1903 in St George Hanover Square district.