Thomas arrived in France on the 15th December 1916 and joined the Battalion in the field on the 7th January 1917. He was admitted to hospital on the 13th March 1917, suffering from Influenza and spent most of the month recovering. He returned to the Battalion on the 28th March 1917 and was reported missing during the Third Battle of Ypres, or Battle of Passchendaele as it more commonly known. The offensive was launched on 31st July 1917 and continued until the fall of Passchendaele village on 6th November 1917. The Battalion marched from Vlamertinge to their assembly position arriving by midnight on the 30th/31st July 1917.
The 1st Hertfordshire Battalion were in support of an attack on the Langemarck Line and a general bombardment of the German lines commenced at 3.45am on the 31st July and and the planned assault began. It had three objectives to achieve known as Blue, Black & Green and units of the 116th Brigade easily captured the first two objectives, preparing the way for the forward companies of the Hertfordshire battalion, to take the third objective. At 05.00am the hertfordshires left their assembly positions to attack their objective, which lay over the crest of a ridge.
As they made their way forward they came under heavy fire from both German machine guns and snipers but after eliminating a German strongpoint moved up towards St.Juliaan, which was only lightly held. The battalion crossed the Steenbeek with some difficulty and two of its supporting Tanks became bogged down in the mud. Things then went from bad to worse. A pre-arranged artillery barrage never materialised due to the guns being unable to move forward over the muddy terrain and the German barbed wire defences, which were fifteen feet deep in some places, were found to still be intact. It was soon realised that ground could only be won by section " rushes" supported by the unit’s own fire.
The Cheshire Regiment were on the right of the battalion but the Black Watch, who were due to cover the left flank, had been seriously delayed. This left the Hertfordshire Regiment seriously exposed and the Germans exploited this by bringing a hurricane of fire down upon the stricken troops. This was followed by a German counter-attack and by 10.30am it was clear that the objective could not be achieved. Casualties were very heavy with 459 men being killed, missing or wounded.
Thomas has no known grave and his name is recorded on the Menin Gate Memorial, Ypres, Belgium.
Mary and the children returned to her birthplace in Clapton, London.