The regiment remained in the Gibraltar garrison for several years, and was present when Spain declared war on the United Kingdom in June 1779 and the Great Siege of Gibraltar began. At this point, the effective regimental strength was 560 men and 27 officers, around a tenth of the garrison. A relief convoy arrived early in 1780, and a second in April 1781, but supplies remained limited. The commander of the garrison decided late in 1781 to attempt a sortie, and this was launched on the night of 26 November; the flank companies of the 56th were part of the raiding force, and successfully destroyed several batteries of artillery.