He then had a variety of farming positions, was a Territorial and when he enlisted on the 30th of November 1916 he was a Station Manager at Oliver Smith’s property at Landsdowne. Spencer commenced duty on January 8th, 1917 at the Featherston, Military Camp, and embarked on the Pakeha 26th April 1917 from Wellington for Plymouth, England. He arrived in Etaples, France on the 19th of October 1917 and was posted to the 3rd Battery of the 1st Brigade NZFA on the 12th of November. The Division spent a busy winter in the Polygon Wood of Becalaere sector at Ypres.

Spring saw the Division rushing in to help against the German offensive on the Somme and heavy fightng continued as the Germans fell back on the Hindenburg Line, and it was there Spencer was wounded on the 5th of October 1918 near La Vacquerie. He rejoined his unit and on the 11th of October the 1st Brigade crossed the River Selle, the Division then advanced 11 miles in five days. On the 2nd of November Spencer was posted on leave to Scotland. While the Division went on to take the mediaeval fortress of Le Quenoy on the 4th of November – the War ended seven days later.

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While in Glasgow he caught influenza and was hospitalized in Brockenhurst, Codford and Stubhill. During his convalescence he made many friends who corresponded with him following his return to New Zealand on the Raranga arriving on the 20th of March 1919. He was discharged from War Service on the 27th of May 1919. He married Ethel Louisa Hawke of Clareville in 1921 and they had four children, sadly all died in childhood. Spencer married Alice Wright nee Revell in 1973, he died on the 1st of May 1985 and is buried in Clareville Cemetery