The family returned home once for the Lambeth Conference in 1897, and Bernard and his brother Harold were educated for a term at The King's School, Canterbury. In 1901, Bishop Montgomery became secretary of the Society for the Propagation of the Gospel, and the family returned to London. Montgomery went to St Paul's School and then the Royal Military Academy, Sandhurst, from which he was almost expelled for setting fire to a fellow cadet during a fight with pokers. On graduation he joined the 1st Battalion, The Royal Warwickshire Regiment in September 1908 as a second lieutenant, first seeing service in India until 1913. He was promoted to lieutenant in 1910.
The First World War began in August 1914 and Montgomery moved to France with his regiment that month. Half his battalion was destroyed during the retreat from Mons. At Méteren, on 13 October 1914, during an Allied counter-offensive, he was shot through the right lung by a sniper and was so badly injured that a grave was dug because he was expected to die.
A Platoon sergeant came to assist him but was killed. He fell on Montgomery. The German sniper fired at him until sunset. The body of the sergeant protected Montgomery and took most of the enemy fire. Montgomery was hit once more though, in the knee. He was awarded the Distinguished Service Order for gallant leadership. The citation for this award, published in the "London Gazette" in December 1914 reads:
In early 1915, he was appointed to be brigade major training Kitchener's New Army and returned to the Western Front in early 1916 as an operations staff officer during the battles of the Somme, Arras, and Passchendaele. During this time he came under IX Corps, part of General Sir Herbert Plumer's Second Army. Because the infantry, artillery and engineers were trained together, rehearsed together, and worked together they were able to do what they were asked efficiently and without unnecessary casualties.
Montgomery served at the battles of the Lys and Chemin-des-Dames before finishing the war as General Staff Officer 1 and effectively chief of staff of the 47th (2nd London) Division, with the temporary rank of lieutenant-colonel. A photograph from October 1918 shows the then unknown Lt.-Col. Montgomery standing in front of Winston Churchill (Minister of Munitions) at the victory parade at Lille.
Britain declared war on Germany on 3 September 1939. The 3rd Division was sent to Belgium as part of the British Expeditionary Force (BEF). Montgomery predicted a disaster similar to that in 1914, and so spent the Phoney War training his troops to retreat safely rather than offensive operations. During this time, Montgomery faced serious trouble from his superiors for his attitude regarding the sexual health of his soldiers. However, he was defended from dismissal by his superior Alan Brooke, commander of II Corps. Montgomery's training paid off when the Germans began their invasion of the Low Countries on 10 May 1940 and the 3rd Division advanced to the River Dijle and then withdrew to Dunkirk with great professionalism, returning to Britain intact with minimal casualties. During Operation Dynamo — the evacuation of 330,000 BEF and French troops to Britain — Montgomery had assumed command of the II Corps after Brooke had taken acting command of the whole BEF.
On his return Montgomery annoyed the War Office by criticising the way the BEF was run and he was put in charge of a smaller group of soldiers. He was however made a Companion of the Order of the Bath. In July 1940, he was appointed acting lieutenant-general, placed in command of V Corps, responsible for the defence of Hampshire and Dorset, and started a long-running feud with the new commander-in-chief, Southern Command, Claude Auchinleck. In April 1941, he became commander of XII Corps responsible for the defence of Kent. During this period he instituted a regime of continuous training and insisted on high levels of physical fitness for both officers and other ranks. He was ruthless in sacking officers he considered would be unfit for command in action. In December 1941 Montgomery was given command of South-Eastern Command overseeing the defence of Kent, Sussex and Surrey. He renamed his command the South-Eastern Army to promote offensive spirit. During this time he further developed and rehearsed his ideas and trained his soldiers, culminating in Exercise Tiger in May 1942, a combined forces exercise involving 100,000 troops.
In 1942, a new field commander was needed in the Middle East. Auchinleck was acting as both the commander-in-chief Middle East Command and commander Eighth Army. He had fixed the Allied position at the First Battle of El Alamein, but after a visit in August 1942, the Prime Minister, Winston Churchill, replaced him as C-in-C with Alexander and William Gott as commander of the Eighth Army in the Western Desert. After Gott was killed flying back to Cairo Churchill was persuaded by Brooke, who by this time was Chief of the Imperial General Staff to appoint Montgomery, who had only just been nominated to replace Alexander as commander of the British ground forces for Operation Torch.
Montgomery was very popular with the men of the Eighth Army, and when he took command Army's fighting spirit and abilities got better. Taking command on 13 August 1942, he immediately became a whirlwind of activity. He ordered the creation of the X Corps, which contained all armoured divisions to fight alongside his XXX Corps which was all infantry divisions. This was in no way similar to a German Panzer Corps. One of Rommel's Panzer Corps combined infantry, armour and artillery units under one division commander. The only common commander for Montgomery's all infantry and all armour corps was the Eighth Army Commander himself. Correlli Barnett said that Montgomery's solution "...was in every way opposite to Auchinleck's and in every way wrong, for it carried the existing dangerous separatism still further." Montgomery spent two months making the long front line at El Alamein stronger. He asked Alexander to send him two new British divisions (51st Highland and 44th) that were then arriving in Egypt and were scheduled to be deployed in defence of the Nile Delta. He moved his field HQ to Burg al Arab, close to the Air Force command post in order better to coordinate combined operations. Montgomery wanted the Army, Navy and Air Force to fight together from the same detailed plan. He ordered immediate reinforcement of the vital heights of Alam Halfa, just behind his own lines, expecting the German commander, Erwin Rommel, to attack with there, something that Rommel soon did. Montgomery ordered all plans for retreat be destroyed. "I have cancelled the plan for withdrawal", he told his officers at the first meeting he held with them in the desert. "If we are attacked, then there will be no retreat. If we cannot stay here alive, then we will stay here dead."
Montgomery made a great effort to appear before troops as often as possible, frequently visiting various units and making himself known to the men, often arranging for cigarettes to be distributed. Although he still wore a standard British officer's cap on arrival in the desert, he briefly wore an Australian broad-brimmed hat before switching to wearing the black beret (with the badge of the Royal Tank Regiment next to the British General Officer's badge) for which he became notable. The black beret had been given to him by a soldier when he climbing into a tank to get a closer look at the front lines. Both Brooke and Alexander were astonished by the change in atmosphere when they visited on 19 August, less than a week after Montgomery had taken command.