After the failed Rebellion of 1837 in Upper Canada, its leader, William Lyon Mackenzie, retreated to Navy Island, in the Niagara River, accompanied by some 200 followers. The Caroline, an American ship based at Fort Schlosser in New York State, was chartered to bring supplies to the rebels. On 29 December 1837, a force of the Upper Canada militia led by Commander Andrew Drew of the Royal Navy found the Caroline moored at Schlosser. In the quick skirmish that followed, an American was killed. The Caroline, set on fire and adrift, capsized before reaching the falls and sank. The incident aggravated the already tense relationship between the United Kingdom and the United States.