The Governor and Council of the British India Company at Madras having heard that Lally had sent a detachment of his forces southward and threatened Trinchinopoli, determined that Colonel Eyre Coote, who had recently arrived in the East, should take the field and drive it back.
The French officers had been fortunate in acquiring the favour of many of the Indian chiefs. Thus in 1755 the King of Travancore employed M. de Launay to discipline 10,000 Naires of Malabar in the mode of the European infantry; and thus M. de Lally, who had won the alliance of Salubetzingue, sovereign of the whole country, expected the arrival of his brother Bassuletzingue with a column of 12,000 Indians. When more than a hundred miles distant from the French army, the prince sent a Rissaldar to request that an officer of rank with a body of French should be sent to facilitate their junction. Lally immediately despatched the Marquis de Bussy on this service, with a detachment which joined the prince beneath the walls of Arcot. In twelve days all that was necessary might have been done; but the loitering marquis spun out the time to no less than two-and-forty. While Lally was totally unable to account for his absence, a dangerous ferment arose in the camp of Prince Bassuletzingue, there being no pay for his soldiers, as M. d'Aché's diamonds were yet unsold; and during the delay the British troops under Colonel Coote (aware that Lally could not begin a campaign without cavalry) suddenly made themselves masters of Vandivash on the 30th November, after having breached the walls. Thus, by the indolence of M. de Bussy one of the most important fortresses on the coast was lost, and its garrison of 900 men taken, with forty-nine pieces of cannon and a vast quantity of ammunition.
On the 10th December they took Cosangoli, which was bravely defended by a mixed garrison of French and sepoys under Colonel O'Kennely, an Irish officer; who, after his guns were dismounted, capitulated and marched out with all the honours of war. With 100 Frenchmen he joined Lally, but 500 of his sepoys were disarmed and dismissed by Coote.
The double and dangerous success of this vigilant and enterprising officer compelled Lally to attempt a decisive demonstration for the recapture of Vandivash; but Coote, who had completely superseded Brereton in the command, was an officer who ably defended the conquests his bravery had made.
Having now somewhat recovered his health and strength, on the 10th January, 1760, the Lieutenant-General du Roi marched towards the captured fortress at the head of 2200 Frenchmen, and about 10,000 native troops. Among the latter were 1800 blacks called the Regiment de Bussy, 300 Caffres, and 2000 cavalry obtained from a Mahratta chief, with whom Lally had concluded a treaty, as soon as he found himself disappointed by Prince Bassuletzingue. They were all clothed and armed after the picturesque fashion of their native country (which extends across the whole peninsula of Hindostan) and were led by a Rissaldar, or commander of independent horse. He had twenty-five pieces of cannon with him.
He came in sight of the British on the banks of the Poliar, a broad and sandy river, the bed of which was quite dry; though in the middle of October, when the winter usually commences, and the rain descends in torrents, the river is sometimes half-a-mile broad, and flows towards the ocean with the greatest fury. There the adverse hosts hovered in sight of each other, until after succeeding in destroying some magazines which were in Colonel Coote's rear (the loss of which prevented his troops from acting in the field for some days after), Lally with his 12,000 men suddenly invested Vandivash, against which his batteries opened with such effect, that a broad and practicable breach was soon made in the outer bastion, and now it was hoped that by one bold assault the captured fortress would be re-won, and with it the entire disputed territory.
But at the very time when Lally was about to lead on the assault, Coote with 1700 European and 3000 black troops, fourteen pieces of cannon, and one howitzer, came suddenly upon his rear to relieve the garrison.
Exposed to the cannon of the fort on one side, and to the troops of Coote on the other, Lally found himself critically situated; but, turning like a lion at bay, he drew off from his trenches, and rapidly formed in order of battle to face this new enemy, on the 21st of January.
Both armies were in high spirits and eager to engage.
About nine in the morning they were two miles apart. Coote having advanced with his cavalry and five companies of sepoys, Lally sent forward his Mahratta horse to meet them; but these, on being galled by two pieces of cannon, retired with precipitation. During this the colonel had succeeded in completely reconnoitring the position of Count Lally, whose forces were ably and judiciously placed, till the British made a movement to the right, which obliged him to alter and extend his left flank.