Samuel received his medical education in Dublin, qualifying M.B., Ch.B. in 1912 and M.D. in 1913. He took up a commission at the rank of Lieutenant in the R.A.M.C., Special Reserve on 17th September 1914. He gained promotion to the rank of Captain on 11th April 1915. On 4th May 1915 he arrived in Aldershot, reporting himself for duty with No 17 Casualty Clearing Station. He then sailed with the unit to Havre on S.S. St Petersburg, entering the war in France on 21st May 1915. On 26th July 1915 he was serving with a sub-section of the unit sent to Remy Siding with two other officers and 20 rank and file. On 22nd October to 30th November 1916 he served with No 29 Casualty Clearing Station on temporary duty, and on 5th March 1917 took over temporary command of R.C.E. II. He reported sick on 10th July 1917 and was evacuated to hospital. He relinquished his commission on account of ill-health on 8th March 1919 but retained his rank of Captain.