He played a key part in setting up the Ulster Volunteers as a unionist militia during the Home Rule crisis of 1912, and was believed to have organised gun-running.
He took part in the action at Fort Gamaizah (near Suakin), and served with the Nile Frontier Force in 1889 winning the Order of Medjidie Third Class.
[9] He accompanied the expedition to Dongola in 1896, taking part in the operations of 7 June (in which his horse was again shot) and 19 September; on 3 November 1896 he was mentioned in despatches.
According to Timothy Bowman's history, Hacket Pain was among a select group of senior officers specifically recruited by the Unionist establishment.
[19] His appointment as chief of staff to Lieutenant-General Sir George Richardson, the General Officer Commanding of the Volunteers was announced in September 1913.
[23] Just as the Ulster Volunteers knew they needed armaments, the British authorities were keen to stop them from landing guns on Irish shores.
At the end of March 1914, just as the Ulster Volunteers were readying for an imminent civil war, a Norwegian steamer called Fanny was filled full of 35,000 rifles from Germany, and gave its destination as "Öreland" (sic).
The Ulster Volunteers had been given a general mobilisation order on Friday 24 April and made sure that all roads leading to the disembarking centres had been blocked and that key telephone wires had been cut.
[18] Timothy Bowman's history notes that Hacket Pain was given the credit but that Fred Crawford, who organised the shipment, regarded him as a 'dove' in the ruling councils of the Volunteers.
The Army welcomed the fact that the Volunteers were trained and armed, and Hacket Pain was appointed on 4 September to command the 108th Infantry Brigade in France.
Nationalist MP Joseph Devlin complained that this meant the chief of staff in Carson's army was responsible for protecting Roman Catholics.
[39] Retiring at the general election in October 1922, Hacket Pain lived at the United Services Club in Pall Mall for a short time.
[40] In October 1923 he was taken ill and became a patient at King Edward VII Convalescent Home for Officers at Osborne House on the Isle of Wight.