First World War
Following the outbreak of war in August 1914, Seely was recalled to active duty as a special-service officer. Seely served for near the entirety of the First World War, with few breaks, leaving London on 11 August 1914 to take up a post on Sir John French's staff. On a liaison mission between the French Fifth Army and Haig's I Corps (31 August 1914 – during the period when Sir John French's retreat had opened up a gap in the Allied line), he claimed to have been almost captured in the fog, but to have bluffed his way past a German cavalry patrol by calling out (in German) that he was a member of the Great General Staff.
In October 1914, Seely was dispatched to Belgium to participate in the Siege of Antwerp. Initially acting as an observer, Seely temporarily joined the staff of Archibald Paris, the commander of the British Royal Naval Division, which had been deployed to the city under orders from First Lord Winston Churchill. Seely's Orderly Officer in the Siege of Antwerp was Archibald Alexander Gordon, alias Major Gordon, who with him surveyed the British and Belgian frontlines. When the situation became critical, Seely contacted Lord Kitchener by phone and later received orders for a massive evacuation of the British forces to Ostend. Once it became clear Antwerp was going to capitulate to the Germans, Seely assisted with the evacuation of the Royal Naval Division.
On 28 January 1915, Seely was given command of the Canadian Cavalry Brigade, with the temporary rank of brigadier-general and the substantive rank of colonel. He was mentioned in despatches five times, further enhancing his reputation for bravery. He was known as "the Luckiest Man in the Army" and was the subject of many apocryphal stories, such as that he recommended his soldier servant for a Victoria Cross for having stood never less than twenty yards behind him during an engagement.
On 1 January 1916, he was appointed a Companion of the Order of the Bath (CB). During the advance to the Hindenburg Line in spring 1917, Seely, whose brigade was attached to Fourth Army, commandeered infantry from XV Corps to form an ad hoc combat group to capture Équancourt. General du Cane's anger was assuaged – Seely later claimed – by the arrival of congratulations from Field Marshal Haig. He was appointed a Companion of the Order of St. Michael and St. George (CMG) on 1 January 1918.
During the German Spring Offensive Seely, back from London, called on Percy Beddington, a senior staff officer of the Fifth Army, at around 2am on 24 March 1918, to inform him of the gossip in London that Fifth Army had been routed. Beddington, who had only managed to get to sleep an hour previously, for the first time since the morning of 21 March, on a camp bed in his office, recorded that he "lost (his) temper, cursed him up hill and down dale for daring to wake (him) with such drivel." Seely himself later admitted that it suddenly seemed unimportant a few days later when he was commanding the CCB in action, but it mattered a great deal in the next few days when Gough was sacked from command of the Army as a scapegoat.
After being gassed in 1918, he returned to England, and was relieved of command of the brigade on 20 May 1918. He was angry about the move.
Seely had remained an MP throughout his military service in the First World War, and as a member of the Liberal faction which supported Lloyd George's coalition government, he was appointed Parliamentary Secretary to the Ministry of Munitions on 10 July 1918, serving under Churchill (then Minister of Munitions).
He was the only member of the government, besides Churchill, to see active service in the war, and was promoted to the temporary rank of major general on 13 July. Belgium appointed him a Commander of the Order of the Crown, and France both appointed Seely a Commander of the Légion d'honneur and awarded him the Croix de guerre.
