Vernon crossed to France in July 1915. At the beginning of August both he and his cousin William spent almost a week in billets at Haverskerque before moving to billets near Merville. (map). It was very hot and for over two weeks Vernon's regiment was mainly occupied with parades, route marches and night marches. Following a terrific thunderstorm - poplars beside the nearby canal were struck - the battalion marched south to Vieille Chapelle where training in trench warfare began in earnest. By the end of August they marched further south to Gorre and went into the trenches just north of Festubert, mainly to work on the dugouts and carry out repairs. The Germans were working hard at the end of their old trench running from Barnton Road to their line; British machine-gun fire dispersed their working parties on at least one occasion. There were some exchanges of gunfire and a few shells fell on the British trenches, one near Goldneys Keep (see the sketch of the scene of battle copied from the battalion war diary). Although there was only limited hostile activity the battalion suffered several casualties and one man was killed. On 10 September the battalion was relieved and spent ten days in Brigade reserve on working parties before returning to the forward trenches. Even in reserve shellfire could reach them; one man was injured and an enemy aeroplane was brought down beside them.
Everything changed when from 21 to 24 September the mighty barrages from the British artillery heralded the Battle of Festubert, described in detail here. Extracts from the regimental diary of Vernon’s regiment are included there and describe the death of his CO, Lt. Col. Madocks, on 25 September during the attempted advance, and the heavy losses suffered by 9th Royal Welsh Fusiliers. Vernon's cousin William Henry Kenrick Owen’s of the Welsh Regiment was among those mortally wounded. A former tutor at Bangor University reported (here) on the battle and mentioned Vernon.
After the remnants of Vernon's battalion had reformed the men were withdrawn to the Intermediate Line about a mile back where the mud still made conditions extremely uncomfortable. They had been in the trenches with barely a break since August though they had spent very brief interludes in billets at, for example, Vieille Chapelle and Locon (map). On 30 September the men had "a very trying" march from Locon to the trenches near Cabrin (map); it was cold and wet and delayed by congestion en route. They spent a short time in reserve in the neighbourhood of some extremely noisy British batteries. One of their duties was to carry gas cylinders, weighing 150 lbs each, over muddy, shell-damaged roads to the front trenches. Otherwise the battalion’s activities involved cleaning, restocking, training and providing working parties for the forward area. Maj. Gen. Gasken, GOC 19th Division, inspected them and congratulated them on their part in the action of 25 September.