This sortie postponed the great Spanish assault for several months. In that time the British began building an extensive tunnel network through the Rock of Gibraltar. The work was carried out by hand, aided by gunpowder blasts, which was dangerous. It took thirteen men five weeks to dig a tunnel with a length of . Embrasures were blasted overlooking the Spanish lines. Additionally, a new type of cannon mount was invented that allowed a cannon to fire at a downward angle: the new depressing gun-carriage devised by George Koehler allowed guns to be fired down a slope. This was demonstrated on 15 February 1782 at Princess Royal's Battery. This new carriage enabled the defending guns to take advantage of the height of the Rock of Gibraltar: they could strike out far, but also be angled downward to fire on approaching attackers.