The battle of St. Thome (4 November 1746) was the second of two victories in three days in which small French armies defeated the larger army of the Nawab of the Carnatic (First Carnatic War).
The British and French East India Companies both had important bases in the south of India, at Madras and Pondicherry. These bases were in the territory ruled by Anwar-ur-Din, the Nawab of the Carnatic, the Mughal governor in the area. When fighting broke out between the British and the French (part of the War of the Austrian Succession), the Nawab declared his territory to be neutral and forbade the French and British from attacking each others possessions. This enforced truce was broken by the French under Admiral La Bourdonnais, who in September 1746 besieged and captured Madras. The Nawab was placated by the French governor, Marquis Joseph-François Dupleix, who promised to hand Madras over the Nawab once it had been captured.
Admiral La Bourdonnais didn't agree with this plan. Instead he wanted to ransom the town back to its British occupants. The argument between the two men lasted into mid-October, when a storm damaged La Bordonnais' fleet and forced him to sail away. By this point the Nawab had lost patience with the French, and he dispatched a 10,000 strong army under the command of his son Maphuze Khan to besiege Madras.
This army suffered two defeats at the hands of much smaller French forces in only three days. On 2 November the French commander at Madras launched a sortie against Maphuze Khan's army with 400 men and two field guns. The rapid fire of the field guns caused a panic in the Nawab's army, and it fled from the scene.
Maphuze Khan was soon able to regain control of his army, and on 3 November he moved four miles south, to St. Thome, where he planned to block a small French force known to be coming to reinforce the garrison of Madras. Maphuze Khan still had 10,000 men, and he was able to take up a strong position defending a river.
The French force consisted of 250 Europeans and 700 Sepoys, recruited from the local populace, all under the command of a Swiss officer named Paradis. Despite being outnumbered by ten-to-one, Paradis decided to attack across the river. He ordered his men to fire one volley and then charge with their bayonets. This unexpectedly bold attack broke the morale of the Nawab's army, which turned and tried to flee into St. Thome, all the time coming under fire from Paradis' men. The rout was made worse when a force from Madras arrived on the scene and attacked the rear of the retreating army. This time the Nawab's army was broken, and fled back into the heart of his territory.
The battle had two effects. In the short term Dupleix declared Madras to be French by right of conquest, and appointed Paradis to command the city. Madras remained in French hands until the end of the war, when it was returned to the British, who in return handed back Louisburg in Canada. The longer term impact was to make British and French generals realise that they now had a weapon that could defeat the massive Indian armies that had intimidated them until this point - the rapid fire of disciplined troops was now capable of defeating Indian troops, and in particular the highly prestigious cavalry. This discovery would soon help transform the balance of power in India.