In Phase I, which was implemented immediately, REME was formed on the existing framework of the RAOC (E), strengthened by the transfer of certain technical units and tradesmen from the RE and RASC. At the same time, a number of individual tradesmen were transferred into REME from other Corps. The new Corps was made responsible for repairing the technical equipment of all arms with certain major exceptions. REME did not yet undertake:
These repairs which were carried out by unit tradesmen who were driver/mechanics or fitters in regiments and belonged to the unit rather than being attached to it.
Repairs of RASC-operated vehicles, which remained the responsibility of the RASC; thus each RASC Transport Company had its own workshop. Repairs of RE specialist equipment, which remained the responsibility of the RE.
In 1942 the Mechanical Engineering Directorate at the War Office was established under the Director of Mechanical Engineering (DME), Major-General E B Rowcroft (later Sir Bertram Rowcroft). A plan for the subsequent development of the Corps was drawn up in three stages of nine months each and in almost every detail planned target dates were achieved. In India the Indian EME (IEME) was formed, which was separate from REME since, at this time, the Indian Army was a separate organisation although many officers and technical personnel were British. Also, HQ REME Training Establishment was formed at Arborfield, Berkshire to control REME technical training. Importantly, the repair system in the field was reorganised so that repair could be carried out as far forward as possible and the take-over from RAOC of responsibility for scaling of spares was completed. DMEs and deputies were appointed to all major headquarters of the field army and deputy directors were appointed to all static command headquarters. Commanders REME (CREME) were appointed to divisions and Brigade Electrical and Mechanical Engineers (BEME) to brigades.
Almost at once the new organisation was tried out and proved successful at the 2nd Battle of Alamein; the first major operation after the Corps was formed. The re-organised recovery and repair system was thoroughly tested during the remainder of the war, during which REME grew to be the largest technical corps, extending its activities to include the manufacture of spare parts and special equipment on a large scale. In addition to its uniformed tradesmen, the Corps employed thousands of civilian tradesmen of many different nationalities in its static workshops throughout the world.
REME reached its maximum strength in May 1945, approximately 8000 officers and 152,000 other ranks. The IEME, East and West African EMEs, Royal Canadian, Australian, New Zealand EMEs, and the South African Technical Service Corps (TSC) totalled another 185,000. Some 130,000 civilians were employed in EME Services in all parts of the world.