On 27 November 1781, the night before the launch of the grand attack, the British made their surprise sortie. In all, 2,435 soldiers with 99 officers were involved, organised into three columns of around 700–800 men each, including engineers and pioneers armed with axes and firing equipment. At around 2:00 they marched towards the besiegers' lines. The right column came across the Spanish sentries at the end of the parallel, charged, and stormed the lines, bayoneting the Spanish defenders. While the rest of the defenders retreated, the eastern flank of the Spanish advanced works was taken and consolidated. One detachment of the right column, a group of Hanoverians, got lost in the dark, mistook their target, and found themselves at the base of the huge San Carlos mortar battery. Having realised their mistake, they decided to attack the position, and after some heavy fighting the position was taken. This battery had been the intended target of the centre column, which came up, reinforced the position, and prepared for a Spanish counterattack. Meanwhile the left column struck along the seashore meeting light resistance. The flank companies of the 73rd Highlanders charged ahead, stormed the San Pascual and the San Martín batteries, and took the trenches, putting the Spanish to flight.