View source for Brian Robertson, 1st Baron Robertson of Oakridge

===East African Campaign===
{{main|East African Campaign (World War II)}}
The outbreak of the [[Second World War]] in Europe in September 1939 prompted Hertzog to resign rather than support the war. Robertson was a strong supporter, urging members of the Natal Chamber of Industries to release army reservists. In November 1939, he resigned to rejoin the British Army. He had long assumed that he could easily do so, but the War Office rejected his offer, on the grounds that he was too old. He therefore offered his services to the [[Union Defence Force (South Africa)|Union Defence Force]] (UDF), which accepted him, as it was short of trained staff officers. He was commissioned as a lieutenant-colonel in the [[South African Army]] on 1 February 1940, and was sent to the South African Staff College in May. He passed the course easily, and was ranked first in his class of 23. On 16 June, he embarked for [[Mombasa]].{{sfn|Williamson|1996|p=34}}

[[File:The Campaign in East Africa 1941 E2367.jpg|thumb|left|British troops demolish an Italian monument at Kismayu on 11 April 1941]]
Kenya was threatened by Italy's declaration of war on Britain on 10 June 1940, because Kenya was a British colony, and Italy occupied neighbouring Ethiopia and Somalia. In response to appeals for assistance from Britain, the new Prime Minister of South Africa, [[Jan Smuts]], sent the [[1st Infantry Brigade (South Africa)|1st Infantry Brigade Group]] to Kenya in July, followed by the [[1st Infantry Division (South Africa)|South African 1st Infantry Division]] in November. When Robertson arrived in [[Nairobi]], he joined the staff of Major-General D. P. Dickinson's East Africa Force as its Assistant Quartermaster General (AQMG), working under the Deputy Quartermaster General (DQMG), Colonel Alan Duff.{{sfn|Williamson|1996|p=35}} The Kenya and Uganda Railway had ample capacity to move supplies from the base depots as far as [[Thika]] and [[Nanyuki]]; but these railheads were a long way from the frontier. There were two roads: one from Thika to [[Garissa]] and thence to [[Kismayu]] in Somalia; and one from Nanyuki to [[Wajir]], and thence to [[Bardera]] in Somalia. They were passable only by light vehicles in dry weather, but work commenced on improving them when the war began. Forward supply bases were established at [[Bura, Tana River County|Bura]] and Garissa. The dominant problem was the supply of water; at the bases it was obtained from the [[Tana River (Kenya)|Tana River]], but forward of that it was scarce, and water obtained by boring was brackish.{{sfn|Carter|Kann|1952|pp=137–141}} When not at headquarters, Robertson sited dumps, arranged for water supplies, and investigated delays at the railhead at Thika.{{sfn|Williamson|1996|pp=36–37}}

In view of these difficulties, Lieutenant-General [[Alan Cunningham]], who assumed command of East Africa Force on 1 November 1940,{{sfn|Carter|Kann|1952|p=126}} postponed operations until after the spring rains. However, the success of Lieutenant-General [[Richard O'Connor]]'s [[Operation Compass|operation in the Libyan Desert]] and Lieutenant-General [[William Platt]]'s in Eritrea convinced him that the operation could be attempted with fewer troops than he originally contemplated, and the campaign began on 11 February 1941. Kismayu was occupied on 14 February, opening up a sea line of communications to replace the road from Thika.{{sfn|Carter|Kann|1952|pp=142–144}} This was followed by the capture of [[Mogadishu]] on 23 February, but its development as a port was delayed because the Royal Navy had sown the harbour with [[magnetic mines]], which it lacked the ability to clear. The small port of [[Merca]] was therefore developed as a temporary base until Mogadishu was opened in March. The offer of rewards to local civilians for the disclosure of the whereabouts of fuel supplies yielded {{convert|350000|impgal|L}} of petrol and {{convert|80000|impgal|L}} of [[aviation spirit]].{{sfn|Carter|Kann|1952|pp=145–147}}

There was no respite for Duff and Robertson to accumulate supplies, as Cunningham decided to press on to [[Addis Ababa]]. To support this, a new line of communications was opened from [[Berbera]], on the [[Gulf of Aden]], thereby saving {{convert|540|mi}}.{{sfn|Carter|Kann|1952|pp=145–147}} Robertson reported to Cunningham that "the distance from Mogadishu to Berbera was 600 miles. A very fine tarmac road was marked on Italian maps but did not exist after a few miles out of Mogadishu."{{sfn|Williamson|1996|p=38}} Addis Ababa was captured on 6 April.{{sfn|Carter|Kann|1952|pp=148–149}} Robertson flew up to the headquarters of the [[1st (African) Division|11th]] and [[2nd (African) Division|12th African Division]]s on 12 April, and was bombarded with urgent requests, which he struggled to fulfil.{{sfn|Williamson|1996|p=38}} Despite the difficulties, the new Berbera line of communications carried an average of  {{convert|450|LT}} per day between 18 May and 6 July,{{sfn|Carter|Kann|1952|pp=148–149}} by which time the Italians had surrendered. In his report, Cunningham wrote of Duff and Robertson: "I found them undaunted by the magnitude of the demands made on them. That throughout the vicissitudes of bad roads and ports without appliances, ample supplies were able to keep up with the troops, must be accounted a fine achievement by these two officers."{{sfn|Williamson|1996|pp=40–41}} Robertson was mentioned in despatches.<ref>{{London Gazette |date=26 December 1941 |issue=35396 |page=7363}}</ref>