I believe he was not a serving officer but a war correspondent. So I can take some liberties in that regard.
Was he not both? One of the controversies is that he was disliked by his fellow subalterns for reporting on the uglier sides of the war, while serving in that war! I recently watched the series on him, quite good, and he went in and out of the military at will.
Wikipedia Quote: Anticipating the outbreak of the Second Boer War between Britain and the Boer republics, Churchill sailed to South Africa as a journalist for the Morning Post.[52][53] In October, he travelled to the conflict zone near Ladysmith, then besieged by Boer troops, before heading for Colenso.[54] At the Battle of Chieveley, his train was derailed by Boer artillery shelling, he was captured as a prisoner of war (POW) and interned in a POW camp in Pretoria.[55] In December, Churchill escaped and evaded his captors by stowing aboard freight trains and hiding in a mine. He made it to safety in Portuguese East Africa.[56] His escape attracted much publicity.[57]
In January 1900, he briefly rejoined the army as a lieutenant in the South African Light Horse regiment, joining Redvers Buller's fight to relieve the Siege of Ladysmith and take Pretoria.[58] He was among the first British troops into both places. He and cousin, Charles Spencer-Churchill, 9th Duke of Marlborough, demanded and received the surrender of 52 Boer prison camp guards.[59] Throughout the war, he publicly chastised anti-Boer prejudices, calling for them to be treated with "generosity and tolerance",[60] and afterwards urged the British to be magnanimous in victory.[61] In July, having resigned his lieutenancy, he returned to Britain. His Morning Post despatches had been published as London to Ladysmith via Pretoria and sold well.[62]