On 21st August 1914 the 1st Devons left Jersey, where they had been stationed since 1911, and landed at Le Havre, where they were reinforced by nearly 500 reservists from Exeter.
In September, during their first spell in the line, they suffered 100 casualties from shelling. In October on the La Bassee Canal they supported the badly mauled 1st Dorsets and helped capture Givenchy Ridge. The Devons performed well during a bitter three-week battle but lost two thirds of their officers and a third of their men. From November they occupied Messines Ridge in rain and sleet, often knee- or waist-deep in mud and icy water.
On 21st April 1915 they occupied Hill 60, which had been captured on 17th April. Counter-attacks and heavy shelling cost them more than 200 casualties.
On 31st July 1915 they moved to the Somme. When the offensive began on 1st July 1916 the Devons were at Arras but returned to the Somme, to consolidate the line around Longueval. Shellfire and German counter-attacks cost them 265 casualties. In September they made two very successful advances near Guillemont at a cost of 376 casualties.
In the Battle of Arras, in April and May 1917, their losses in four attacks nearly wiped out the Battalion. Near Passchendaele in early October they attacked Polderhoek and suffered 327 casualties. A month later, supporting another attack at Polderhoek, a single company lost another 100 killed and wounded.
In November 1917 the Devons were sent to Northern Italy, where the Italians had been routed at Caporetto. Here they held the line near Vicenza and served on the Piave front before the German onslaught in France in March 1918 caused their return to the Somme.
In mid-April 1918 the 1st Devons held a salient near Nieppe, successfully defending their positions against repeated German counter-attacks. They remained around Nieppe until late July. In August the German army began to fall back and the Devons took part in the rapid Allied advances that characterised the rest of the war. Between 21st and 31st August they attacked and captured German positions, repulsing some fierce counter-attacks. During one German attach on 22nd August Lance-Corporal George Onions and Private Henry Eades alone took 200 German prisoners. Onions received the Regiment’s second Victoria Cross of the War and Eades the Distinguished Conduct Medal. But those ten days cost the Devons 263 casualties.
In September and October they suffered fewer casualties in successful attacks near Beauchamp and Ovillers, where despite a gas attack and terrible weather, they were the first battalion in their division to reach their final objective. Their last action was in the final week of the war beyond the Sambre Canal, when they advanced under heavy shell and machine gun fire, losing 19 killed and more than 60 wounded.
Except for their five months in Italy, the 1st Devons served continuously in France from August 1914 until November 1918 and earned them 26 battle honours. The war had cost the Battalion – whose total strength at any one time should have been 800 men – more than 1,150 killed and three times that number wounded.