It was the Anglo-Zanzibar War, fought between the United Kingdom and Zanzibar. It began at 09:00 (East Africa Time) on 27 August 1896 and ended at 09:40 on 27 August 1896.
That means even this war lasted longer, with a runtime of 94 minutes.
The primary reason for the war was the death of the pro-British Sultan Hamad bin Thuwaini and the succession of Sultan Khalid bin Barghash,who the British were not so fond of.
As part of a treaty signed in 1886, any potential sultan had to first seek permission from the British consul.
As Sultan Already-Forgotten-His-Name did not fulfil this requirement, the British used it as a casus belli (latin term meaning the justification of war – bonus learning!) and sent an ultimatum ordering that the Sultan stand down and leave the palace.
The ultimatum expired at 09:00 and the British decided it was time for action.
Around 2,800 Zanzibaris defended the palace; most were recruited from the civilian population, but they also included the sultan’s palace guard and several hundred of his servants and slaves.
The sultan’s forces sustained roughly 500 casualties, while only one British sailor was injured.
After 40 minutes a ceasefire was called. Sultan Whats-his-name received asylum in the German consulate and the British installed their favoured Sultan as the head of a puppet government. The war marked the end of Zanzibar’s sovereignty and the start of a long period of heavy British influence. All sounds a bit familiar really.
Here’s a war letter that I found from one of the British troops written home to his beloved wife, during the long campaign: