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The Sultan of Zanzibar, a convenient ally for London, died on August 25th, 1896. His cousin Khalid bin Barghash occupied the palace and proclaimed himself successor without asking the British consul, who had another candidate in mind. Mistake.
The British issued an ultimatum: leave the palace by nine in the morning on the 27th. Khalid barricaded himself in with some three thousand men. At 9:02, the warships anchored off the harbour opened fire. By 9:40, the palace was burning, the flag had fallen and Khalid had slipped out the back door towards the German consulate.
Around 38 minutes: it is still considered the shortest war in history. The new sultan, chosen by London, was ruling that very same day.
And there was a bill: Zanzibar was made to pay even for the shells that had been fired at it.