Thomas fought in the First World War, arriving on the Western Front from India with II Battery, XIII Brigade, Royal Field Artillery, part of the 7th (Meerut) Division, in October 1914. Still a second lieutenant when war began, Thomas rose rapidly in rank, being made a lieutenant on 9 June 1915,[4] a temporary captain on 12 January 1916[5] (made permanent on 20 December 1916,[6] four years since he was commissioned), and an actingmajor on 10 April 1917,[7] which he held for only five days, but he regained the rank on 15 June,[8] which he held until 2 October, when he again reverted to his permanent rank of captain.[9] He remained on the Western Front throughout the conflict, was wounded twice, awarded the Military Cross in January 1917[10](and Bar, awarded in September 1917) and Mentioned in Despatches in 1917, and, in January 1918, received the Distinguished Service Order (DSO). The citation for the medal reads:
For conspicuous gallantry and devotion to duty. When his battery was being relieved the position was shelled by an intense bombardment, which lasted for over two hours and caused many casualties in both batteries. The pits and ammunition of one section caught fire, and he succeeded in extinguishing this. Later, the telephone pit and mess shelter were wrecked, and he immediately led the way to the rescue of wounded men inside. The camouflage nets of three more guns were then set alight, and the ammunition began to catch fire. This he also saved by tearing down the burning camouflage and smothering the smouldering ammunition, some of which had already begun to explode. Not until all the fires had been extinguished, and he had seen every man, both wounded and unwounded, clear of the position, did he seek cover for himself. His great gallantry and exceptional coolness throughout the whole of this time were worthy of the highest praise.[11][12][3]
From 22 September he served as a staff captain at the War Office.[3]
In 1931 Thomas served at the Royal Artillery depot at Woolwich, Kent, before in January 1932 becoming a General staff Officer Grade 2 (GSO2) to GeneralSir David Campbell, the Governor and Commander-in-Chief of Malta.[3] After being promoted to brevet lieutenant colonel on 1 July 1933,[15] he returned to England and attended the Royal Naval College, Greenwich, in 1934.[13] This was followed by serving as a GSO2 at the War Office and later GSO1, being promoted to colonel on 12 May 1938 (with seniority dating back to 1 July 1937).[16][3] Promoted to the temporary rank of brigadier on 14 July 1939,[17] he was appointed Deputy Director for Recruiting and Organisation at the War Office, shortly before the outbreak of the Second World War, and then he was Director of Organisation at the War Office in 1940, by which time the war had begun.[12]
In June 1942, three months after Thomas became GOC, the 43rd Division was one of many selected to be converted into a "mixed" division, of one tank brigade and two infantry brigades. As a result, Brigadier Manley James's 128th Brigade left the division and was replaced by the 25th Tank Brigade which, in September, was replaced by the 34th Tank Brigade. Two months later, on 11 November, Thomas was promoted to the permanent rank of major general.[19] In September 1943, however, the experiment with "mixed" divisions was abandoned and, with the arrival of Brigadier Hubert Essame's 214th Infantry Brigade, formerly an independent unit, the division reverted to being a standard infantry division.[1] By this time Thomas's division had been selected to participate in the Alliedinvasion of Normandy, then scheduled to take place in May 1944, as part of the newly formed British Second Army (initially under Lieutenant General Sir Kenneth Anderson but later replaced in January 1944 by Lieutenant General Miles Dempsey), and training in all-arms co-operation, already at a very high standard due to Thomas's energetic and ruthless methods, intensified, and he demanded only the very highest standards.[3][20]
After years of training under Thomas's command, the 43rd Division landed in Normandy in mid-June 1944, but was not immediately involved in any major engagements. However, casualties had already been sustained, by the 43rd (Wessex) Reconnaissance Regiment, commanded by Lieutenant Colonel Francis Lane Fox−who "Von Thoma" later sacked−which suffered severe losses before it even landed in Normandy. On 24 June, the 43rd Division was reassigned from Ritchie's XII Corps to Lieutenant General Sir Richard O'Connor's VIII Corps and, days later, took part in Operation Epsom, in an attempt to capture Caen, which, although a D-Day objective for the 3rd Division, still remained in enemy hands.[21] The division only played a relatively minor role in the operation but played a major role in Operation Jupiter, the British attempt to capture Hill 112. The operation, which commenced on 10 July and ended the following day, was ultimately a British victory, but cost Thomas's division, along with the armoured support in the shape of Brigadier Michael Carver's 4th Armoured Brigade, almost 2,000 casualties.[21] Carver later described Thomas as, "a small, fiery, very determined and grim gunner, without a spark of humour, he would bite the head off anyone who attempted to disagree with him or question his orders."[1][13]
Transferring back to Ritchie's XII Corps, the division had little time for rest for its next battle, the Second Battle of the Odon. The operation was unable to fully achieve its objectives, costing the division further casualties it could ill-afford. It had, however, drawn the attention of the German panzer divisions away from the American front and onto the British front.[22]
From 27 December 1944 until 28 January 1945, during the Battle of the Bulge in which the 43rd Division played no part, Thomas was temporarily given command of XXX Corps by Montgomery, while Horrocks, the GOC, was away in England to rest.[3][24]
Devine, Louis Paul (2015). The British Way of War in Northwest Europe 1944−5: A Study of Two Infantry Divisions. Bloomsbury Publishing. ISBN978-1-4742-2564-9.
Hamilton, Nigel (1986). Monty: The Final Years of the Field Marshall 1944–1976. McGraw-Hill Book Company.
Mead, Richard (2007). Churchill's Lions: A Biographical Guide to the Key British Generals of World War II. Stroud: Spellmount. ISBN978-1-86227-431-0.