[5] Macandrew served as transport officer to Brigadier-General Alfred Gaselee's 2nd Brigade in the Tirah campaign between 1897 and 1898,[6][7] and was promoted to captain on 10 November 1897.

After several other skirmishes, Macandrew moved to serve in the Transvaal in May, seeing action at the Battle of Doornkop on 29 May and being present at the occupation of Pretoria on 4 June.

[6][9] Macandrew was subsequently appointed intelligence officer on the Delagoa line, east of Pretoria, in July, in which role he continued until September.

At this stage he was assigned as the deputy assistant adjutant-general intelligence (DAAGI) to Major-General Ralph Arthur Penrhyn Clements's column, serving in the Transvaal and to the west of Pretoria.

[15] After his appointment with Haig ended, Macandrew continued on as a staff officer, becoming a deputy assistant quartermaster-general at Headquarters, India, on 6 January 1906.

[17][18] When the First World War began in the summer of 1914, Macandrew was assigned to serve on the Western Front in France as a general staff officer, grade 1 (GSO1) to Major-General Michael Rimington, commander of the 1st Indian Cavalry Division.

[20] In April 1915 Macandrew visited Haig, who was now a full general and in command of the First Army of the British Expeditionary Force (BEF), at his headquarters; Macandrew criticised how his cavalry had been utilised during the recent Battle of Neuve Chapelle and disagreed with the view of other staff officers that the war would continue and be won through trench warfare.

[18][22] The historian Simon Robbins argues that Macandrew's staff work for the corps was sub-par, with his requirement that all orders to divisions be personally approved by him stifling initiative and creating backlogs.

Little occurred for the cavalry in the next two weeks, before a push from Fourth Army on 14 July opened a route for the strategically important High Wood to be taken.

He ascribes the failure to poor communication at corps and army level, resulting in Macandrew's force being sent in too late to be effective, and a lack of brigade and divisional initiative which could have overcome it.

[37] The cavalry were very active in the advance, with Haig particularly praising an action of one of Macandrew's squadrons where, on 27 March, it drove the Germans out of Villers-Faucon and several surrounding villages.

The cavalry divisions were expected to break through gaps in the German line caused by attacking British infantry and tanks.

[40] By the afternoon Macandrew's brigades had reached both Masnieres and Marcoing, and small parts of the division succeeded in crossing the canal.

[46][47] At conferences towards the end of 1917, the British prime minister, Lloyd George, influenced by the failure at Cambrai, argued that the continued use of cavalry on the Western Front was useless, and that the cavalrymen would be of more use in other roles.

When the German spring offensive began in March, the commander of 1st Cavalry Division, Major-General Richard Mullens, who Macandrew had been expected to replace, did well enough that Haig decided not to fire him.

[55] A joint Ottoman-German force attacked a weak point of the British line in the Jordan Valley on 14 July at the Battle of Abu Tellul, being defeated by a counter-charge by the ANZAC Mounted Division.

[56] While this attack was ongoing an Ottoman force of 1,200 cavalry made contact with two of Macandrew's regiments, based between Ghoraniyeh and the Dead Sea.

With the British on the other side of the River Jordan to the Turkish force, Brigadier-General Cyril Harbord of the 15th suggested to Macandrew that his two regiments, the Mysore and Jodhpore Lancers, could attack the Ottomans in a pair of flanking manoeuvres.

[60][61] General Sir Edmund Allenby, the commander-in-chief of the EEF, began in July to plan to destroy the Ottoman Army Group F which faced him in the Battle of Megiddo.

[63] To avoid alarming Ottoman intelligence, the cavalry divisions formed up in secret behind XXI Corps, only moving at night as they took their positions.

[71] Slowed by poor guides and long searches of small villages, the 13th Brigade sent to Nazareth attacked only in the early morning of 20 September.

[72][73] Macandrew's commander, Lieutenant-General Sir Harry Chauvel, was highly disappointed to not have captured Liman, although his headquarters and communications had been almost completely destroyed.

[84][83] Chauvel assumed temporary command of the city on 2 October and Macandrew ordered his staff to not mention the incursion of the previous day.

[87] Travelling slowly in the knowledge that the Ottoman armies had already left the area, Macandrew occupied Rayak and Zahle on 6 October without resistance.

[89] Illness had by this point begun to take a heavy toll on Allenby's troops, with the division following up behind Macandrew, the 4th Cavalry, having to stop its advance because of the amount of disease in its ranks.

[92] Macandrew overestimated the condition of the Aleppo walls and defences, which had been maintained poorly, and chose to surround the city with his force rather than directly assault it.

[95][96] On 26 October, the 15th Brigade advanced north to Haritan and encountered a force of Ottoman soldiers that outnumbered them, with around 3,400 men to Harbord's 500 from two understrength regiments.

[104] In early July he was smoking a cigarette in his pyjamas when he entered a room where his uniform tunic was hanging to dry, having been recently cleaned with petrol.

[108] Morton-Jack suggests that if Macandrew had not died prematurely his good war record would have seen him go on to hold more senior appointments within the British Indian Army, as other cavalry officers such as Barrow and Douglas Baird did, both eventually reaching the rank of general.

[110] Macandrew married Esther Cooper in a ceremony officiated by George James Cowley-Brown at St John's, Edinburgh on 9 August 1892.