In 1779, the British captured the French-controlled port of Mahé, which Tipu had placed under his protection, providing some troops for its defence. In response, Hyder launched an invasion of the Carnatic, with the aim of driving the British out of Madras. During this campaign in September 1780, Tipu Sultan was dispatched by Hyder Ali with 10,000 men and 18 guns to intercept Colonel Baillie who was on his way to join Sir Hector Munro. In the Battle of Pollilur, Tipu decisively defeated Baillie. Out of 360 Europeans, about 200 were captured alive, and the sepoys, who were about 3800 men, suffered very high casualties. Munro was moving south with a separate force to join Baillie, but on hearing the news of the defeat he was forced to retreat to Madras, abandoning his artillery in a water tank at Kanchipuram.