All this and much more information can be found on Steven Fuller's excellent site.

The annual Territorial Army summer camp of 1914 finished with emergency orders for all units to return to their bases and await further instructions. On the 5th August 1914 the entire Battalion was 'embodied' for war service with the East Anglian Division. The soldiers were asked whether they wanted to enlist for overseas duties, with a very high percentage saying 'yes' and the '5th (Reserve) Battalion' was also raised soon afterwards. Initially the Reserve battalion was a 'Home Service' Battalion for those who did not wish to serve abroad, those who were over service age or medically unfit for active duty.

Within a week of being mobilised, the East Anglian Division was at its station in and around Chelmsford in Essex, with the Bedfords being billeted at Romford, Essex. However, the expected move abroad did not follow and in September they were dispersed throughout the East Anglia, to provide home defence and train hard in readiness for overseas duties. The 5th battalion were stationed at Buy St. Edmunds from September 1914. Late in 1914 the Companies forming the active service battalion were also re-organised from the pre war structure of eight Companies to four Companies, called A to D. In January 1915 the 5th Battalion was designated 'The 1st/5th Battalion' and the '5th Reserve Battalion' was re-designated as the '2nd/5th Battalion', serving with the '69th (2nd East Anglian) Division' in the Home Forces until disbanded in February 1918. Later that year the '3rd/5th Battalion' was also raised as a training and draft finding battalion.

In March 1915, the 1st/5th Battalion moved from Bury to Norwich and then to St. Albans in May, where specialist training was stepped up and their formation was re-designated as the 162nd (East Midland) Brigade in the 54th (East Anglian) Division. On the 25th July hot climate uniforms were issued, the battalion were ordered to hurriedly collect all stores and equipment and they set off for the south coast on a series of trains.

The battalion left Devonport on the 26th July 1915, bound for 'somewhere out East' and, after a brief stop-over in Egypt, disembarked on Gallipoli, serving there between 10th August and 4th December. During their assault against the Kiretch Tepe Sirt on 15th August 1915 an observing Staff Officer observed their progress through his binoculars and saw the battalion's metal flashes glinting yellow in the sun as they doggedly advanced. He remarked "By Jove! If only we had one or two more battalions of those yellow devils we should be across the peninsular by tommorow". With that, the battalion's nickname - the 'Yellow Devils' - was born. A pitifully small number of them remained by December 1915 and they were moved back to Egypt to be rebuilt between January and March 1916, after which a year-long posting to guard the Suez Canal followed. The battalion advanced to Gaza with the British and Commonwealth forces in March 1917, taking part in all of the actions there and during the advances through Palestine that followed. By the armistice in October 1918, they were stationed at Beirut, having spent the entire campaign in that theatre of war.

The 54th (East Anglian) Division was comprised the 161st (Essex), the 162nd (East Midland) and 163rd (Norfolk and Suffolk) Infantry Brigades, with the 162nd being composed from:

• 1st/5th Battalion, the Bedfordshire Regiment
• 1st/4th Battalion, the Northamptonshire Regiment
• 1st/1st Battalion, the Cambridgeshire Regiment [left February 1915]
• 1st/1st Battalion, the Hertfordshire Regiment [left November 1914]
• 2nd/1st Battalion, the Cambridgeshire Regiment [between February and April 1915]
• 1st/10th Battalion, the London Regiment [from April 1915]
• 1st/11th Battalion, the London Regiment [from April 1915]

Soldiers in this theatre of war suffered notably from illness, with the battalion losing considerably more men to local diseases than enemy fire. Nevertheless, over 120 gallantry medals were issued to soldiers from the 1st/5th battalion, including a Victoria Cross and the battalion were engaged in the following actions:

The battalion were disembodied in June 1919 whilst stationed at Beirut and reformed in February 1920 at Bedford, as a part time, Territorial battalion again.