By the outbreak of the First World War, Fulton had advanced in rank to major. In New Zealand on leave when the United Kingdom declared war on Imperial Germany on 4 August 1914, he offered his services to the New Zealand government the following day. Made an acting lieutenant-colonel, he was placed in command of the infantry battalion that was to be part of the Samoan Expeditionary Force (SEF) intended to occupy German Samoa. in response to a request of the British government. The SEF sailed from Wellington on 15 August and the Occupation of German Samoa was bloodlessly achieved on 29 August when the New Zealanders landed at Apia. After serving occupation duty for several months, the main contingent of the SEF returned to New Zealand in April 1915.