He was again with the Guards in the Peninsula during the siege of Cadiz, from July to September 1811; in the latter month, he was appointed assistant adjutant general, filling the post until June 1813. He was breveted colonel on 1 January 1812, resigned his Court office on 18 February 1812, and subsequently commanded the Cadiz garrison from July 1813 to April 1814. Capel was promoted major-general on 4 June 1814, lieutenant-general on 22 July 1830, and general in 1846.