The Territorial RE training centres were closed on 31 December 1917 and training was concentrated in a central training organisation, most of the men from Caernarvon being transferred to 5th Reserve Battalion, RE, at Christchurch, Dorset. Once the Third Line had been established, the unfit men and those remaining TF men who had only signed up for Home Service were separated to join brigades of coast defence units (termed Provisional units from June 1915). 9th Provisional Brigade was formed in East Kent from Lancashire units and details from local Home counties units. By September 1915 it included the 9th Provisional Field Company, RE, and the 9th Provisional Signals Section, RE. After the Military Service Act 1916 swept away the Home/Foreign service distinction all TF soldiers became liable for overseas service, if medically fit. The provisional brigades' role thus expanded to include physical conditioning to render men fit for drafting overseas. Late in 1916 the War Office decided to form them into new home service divisions; in November 1916 9th Provisional Bde moved from Margate to Blackpool in Lancashire to form the basis of the new 73rd Division. The provisional units all received new designations based on their parent units: the field company became 648th (East Lancashire) Field Company in March 1917, while the signal section expanded to form 73rd Divisional Signal Company. After assembling in Lancashire, 73rd Division moved in early January 1917 to join Southern Army (Home Forces), stationed in Essex and Hertfordshire. In December that year the War Office decided to break up the division, and this was carried out on 4 March 1918. The signal company was disbanded, but the field company was reorganised as 648th (Home Counties) Army Troops Company, RE, and went to join the BEF on 23 June.  42nd (East Lancashire) Division began to reform at home in 1920, with Lt-Col J.G. Riddick re-appointed CRE on 16 February. When the TF was reconstituted as the Territorial Army (TA) in 1921, the field companies were renumbered 200–203 (East Lancashire). 200 Company was a Field Park Company; in 1924 it was absorbed into divisional RE HQ. The signal company transferred to the new Royal Corps of Signals as 42nd (East Lancashire) Divisional Signals. In 1924 Supplementary Reserve (formerly Special Reserve) companies of the RE were formed, and 104 (East Lancashire) Army Troops Company was attached to the 42nd at Seymour Grove.