The 7th Dorsets came into being at Wyke Regis on 21st November 1914, but cannot be said to have properly formed as a battalion until 30th January 1915. On 10th February Lieutenant-Colonel W.H Biddulph of the Ceylon Planters Rifle Corps was appointed Commanding Officer. At this time the 7th had a large complement of officers – at one stage more than 100 – but relatively few soldiers. Officers and NCOs were sent on courses to prepare them to train reserves to make up the numbers in the Dorset Regiment’s two newly created Service battalions: the 5th & 6th.
On 28th May the Battalion moved to the Hutments Camp at Bovington, and Lieutenant-Colonel F.P Smyly assumed command on 28th June. The Battalion had rapidly filled up with men. In July 460 joined from the 3rd (Special Reserve) Battalion, and the 7th sent out recruiting parties to gather more volunteers. As a result the Battalion were able to carry out their primary task of training reserves, who started to leave in September 1915 destined mainly for the 5th Dorsets, who were in Gallipoli, and the 6th in France.
The 7th Battalion remained in this role at Bovington Camp until August 1916, when the decision was made to disband it. On the 25th 460 men were returned to the 3rd Dorsets and another 215 were sent to the 35th Training Reserve Battalion. In this Battalion, the men of the various units were permitted to retain their regimental badges and, as Colonel Smyly continued in command, the move was not felt so greatly. On 1st April 1917 the 35th Training Reserve Battalion was incorporated into the 53rd Training Reserve Battalion of the Devonshire Regiment cutting ties to the Dorset Regiment.