War was declared at the beginning of August 1914 and Billy applied for a temporary commission in the army on 15 August, aged 20. He seems to have been closer to his father than to his mother but it was she who signed the application form in which he sought to join any unit of the infantry though he stated he could ride a little. In his application for a commission in the Special Reserve of Officers, in answer to the question asking in which unit or branch he wanted to serve, he crossed out his first answer, "Any", and wrote, "The regiment in which I shall be of most use".
He was a clever, bespectacled young man - his vision without glasses was quite poor - and of average height (5ft 7 1/2ins) when he applied. He was accepted on 24 August and joined the 9th Welsh Regiment. The 9th (Service) Battalion was formed at Cardiff in September 1914, as part of K2. (In the first two years of the War there were six major recruiting drives of which K2 was the second.) His cousin, Vernon Elias Owen, joined the 9th Battalion, Royal Welsh Fusiliers, less than three months later and the cousins were to find themselves in the same theatre of war as both regiments formed part of 58th Brigade, 19th (Western) Division, which crossed to France in July 1915 and remained on the Western Front throughout the war.
Billy’s regiment arrived at Le Havre aboard HM transport Monas Queen on 19 July 1915; between July and September more than one hundred and fifty battalions left our shores for France. By train and route marches he reached Haverskerque (map) on 31 July. Training began in August in intense heat. Each company took turns at being instructed in occupying defensive posts and in trench duties near Pont-du-Hem, just south east of Merville. From 31 August to 4 September the Battalion were in reserve, the four companies taking turns to be one of two companies in the intermediate line, one just behind that line and one in Festubert. From then until 25 September they were in the trenches. The weather was now very bad. There were some exchanges of gunfire, a few shells fell on the British trenches and the regiment suffered several casualties.