Isaac returned to Britain in 1915. He was was unable to make a living, so, despite his criticisms of the war, he enlisted in the army and tried to join the medical services.

However, he was judged too short for regular regiments and so was sent to a 'Bantam' battalion (for men under five feet three inches tall) called the 12th Suffolk Regiment. Reportedly, Isaac was unsuited to Army life, being clumsy and absent minded, and he also encountered anti-semitism from officers and soldiers alike. In a letter to his friend Schiff dated October 1915, Isaac wrote:

"I don't mind the hard sleeping the stiff marches etc. but this is unbearable. Besides my being a Jew makes it bad amongst these wretches."

Isaac was eventually transferred to the 11th Battalion, The King's Own Royal Lancaster Regiment (KORL) and by June 1916 he was in the Somme trenches in France.

This colourful patriotic poster (see above) is typical of the period, though it belonged to the 5th Battalion of the KORL rather than Isaac's own 11th Battalion. See a recruitment poster for Isaac's 11th battalion

Below is a detail of Isaac Rosenberg's entry in the official medal rolls for the KORL, it indicates that he received two campaign medals - the Victory medal and the British war medal. Medal rolls are available for viewing at The National Archives. See the research guide British military campaign and service medals.

Apart from a period of six months in the Royal Engineers working to move dead bodies away from the front line, Isaac served with the KORL until his death. It was while in the trenches that he wrote many of his poems. You can read three of his poems on the next page.