In August 1914, on the outbreak of the
First World War, Blackader was in India, commanding the 2nd Battalion of the Leicesters, which was mobilised for service as part of the
20th (Garhwal) Brigade of the
7th (Meerut) Division. The division was sent to France as part of
Indian Expeditionary Force A, seeing its first action in the trenches on 29 October. On 19 December a force under Blackader's command staged a successful attack on the German trenches, though the attack was overshadowed by the beginning of the
German attack on Givenchy the following day, through which the Leicesters remained in reserve.
Garhwal Brigade Major General
Henry Keary, commanding the Garhwals, was promoted to command the
Lahore Division in January 1915, and on 8 January Blackader was given the temporary rank of brigadier general, assuming command of the Garhwal Brigade in his stead. He was promoted to brevet colonel in February. The Garhwals led the first wave of the
Indian Corps' attack at the
Battle of Neuve Chapelle on 10 March, Three of the attacking battalions reached their objectives, but one was delayed by strong resistance; after clearing the last German trenches, the brigade halted to let the second wave pass through. In the attack, two men were awarded the
Victoria Cross, and nine the
Indian Order of Merit, and Blackader was commended by his corps commander, Lieutenant General
Willcocks, who wrote that "I had learned to respect him and to trust in his judgement. The manner in which he handled his brigade at Neuve Chapelle was good to see, and his report ... is written as brave and modest men write". His force had taken heavy losses, however; the trailing battalion on the flank, the 2/
39th Garhwal Rifles, lost over half its men and all its officers. , France, July 1915. Stood not far behind him is Brigadier General Blackader. The brigade repulsed a heavy attack on the morning of 12 March, but settled into a relatively static position thereafter. On 9 May, the Garhwal Brigade was used as a second wave in the first attacks of the
Battle of Aubers Ridge, without success; they saw action again on the night of 15 May, where the leading battalions met heavy resistance and Blackader was forced to call off the attack. After Aubers Ridge, the corps was then rested in a quiet sector until September, when it deployed for the
Battle of Loos. The initial attack was to be made by three divisions, with the Meerut Division leading the attack on the Indian front; Blackader's brigade, with two
Gurkha battalions and the 2nd Leicesters, was on its right flank. Whilst the attack successfully crossed
no-man's land under cover of the barrage, the right flank of the brigade was caught up in defensive wire, and only one battalion successfully made their way into the German trenches; the brigade lost momentum and dug in. The Indian Corps was withdrawn after Loos, and as a result this was Blackader's last major action in command of Indian troops; by the end of November, the Meerut Division had left France.
Ireland Blackader was transferred to command of the
177th (2/1st Lincoln and Leicester) Brigade, part of the
59th (2nd North Midland) Division in January 1916, when he was also made an aide-de-camp (extra) to King
George V. The 59th was a second-line
Territorial Force division, formed from those Territorials and new volunteers who had not volunteered for overseas service. As a result, it was generally undermanned and underequipped, with priority given to equipping its first-line counterpart, and tasked mostly with home defence duties. The 177th Brigade had been formed as the duplicate of the
138th (Lincoln and Leicester) Brigade, with two second-line battalions of the Lincolnshire Regiment (later the
Royal Lincolnshire Regiment) and two of Blackader's own Leicestershire Regiment. The 59th Division was rushed to Ireland in response to the
Easter Rising of April 1916, where Blackader's new brigade saw its first active service. Blackader, as a senior officer, chaired a number of courts-martial, including those of
Éamonn Ceannt,
Thomas Clarke,
Thomas MacDonagh,
Patrick Pearse, and
Joseph Plunkett, five of the seven signatories to the
Proclamation of the Irish Republic. It appears that Blackader found this task difficult; after Pearse's trial, he is reported to have commented that "I have just done one of the hardest tasks I have ever had to do. I have had to condemn to death one of the finest characters I have ever come across. There must be something very wrong in the state of things that makes a man like that a rebel. I don't wonder that his pupils adored him."
38th (Welsh) Division (centre right) speaks with Major General Blackader (centre left) while visiting the division, 13 August 1916. On 21 June, Blackader was ordered to leave the brigade and go to France; he described the news of the unexpected posting as "like a bombshell". On 9 July, when Major General
Ivor Philipps was removed from command of
38th (Welsh) Division, due to the failure of its hitherto limited attacks against Mametz Wood during the early stages of the
Battle of the Somme as well as the poor communication between the division and corps headquarters, Blackader was named as the preferred replacement by Lieutenant General
Sir Henry Horne,
general officer commanding (GOC) of the
XV Corps, the 38th's superior formation. Horne was overruled, and the command was temporarily given to Major General
Herbert Watts, then GOC
7th Division. Under Watts, the division successfully took its objective,
Mametz Wood, though with severe losses; within a week, Watts was back in command of the 7th Division and Blackader had taken permanent command, The division had been raised in the
New Armies in 1914 with a strong sense of
Liberal patronage, and many of its officers had been personally appointed by
Prime Minister David Lloyd George; as a result, political convenience had often taken priority over military competence when selecting officers. Under Blackader, a new officer from outside the Welsh Liberal milieu and able to sack his subordinates as he saw fit, the division's standard improved significantly. It saw service at
Pilckem Ridge in the early stages of the
Third Battle of Ypres, but from September 1917 onwards it was kept on relatively quiet defensive sectors. The division trained through this period, and in April 1918 was able to mount a limited brigade-size attack, which whilst it involved heavy losses was a clear success in a way that would not have been possible two years earlier. . In late May 1918, Blackader, who in January had been promoted to the substantive rank of major general, was relieved of command and replaced by Major General
Thomas Cubitt, a younger officer. This was not apparently due to incompetence or age – the
commander-in-chief (C-in-C) of the
British Expeditionary Force (BEF), Field Marshal
Sir Douglas Haig, had described Blackader's achievements with the 38th Division as "excellent" – but due to illness; according to
Gary Sheffield, he had fallen ill after "being licked by a rabid dog". Under Cubitt's command, the 38th Division would build on its past training and fight through the
Hundred Days Offensive with great success. ==Post-War==