The siege of Santander (22 July-3 August 1812) was a key Anglo-Spanish success on the north coast of Spain, and gave Wellington access to a key supply base during the campaign of 1813.
During the summer of 1812 a British squadron under Captain Home Popham (the ships of the line HMS Venerable and HMS Magnificent (later replaced by the Abercrombie) and the frigates Medusa, Isis, Diadem, Surveillante and Rhin) operated along the north coast of Spain, attacking a series of ports in cooperation with various Spanish guerrilla bands. Popham and his allies captured Lequeitio (21-22 June 1812) and Castro Urdiales (6-8 July 1812), although several attacks on Guetarai and an attack on the fortified village of Portugalete (11 July 1812) all failed.
After the attack on Portugalete, Popham moved west to attack the key port at Santander. He arrived off the port on 22 July, and began a naval blockade. At the same time a Spanish force under José Ramón Rodil Campillo, a regular army officer who now commanded one of the guerrilla bands under Juan Díaz Porlier, blockaded the city from the land. Santander was defended by around 1,600 men under Governor Dubreton.
Popham's first problem was how to get his ships into the harbour, from where they could threaten the city. He landed guns on the rocky island of Mouro, and used them to bombard the castle that defended the entrance to the harbour. On 24 July, after the French fire from the castle had reduced in strength, he ran his ships past the castle into the harbour. The castle was abandoned by the French, and occupied by the Marines.
On 27 July the British and Spanish attempted to storm the city itself. This attack failed at some cost (amongst the wounded were Captain Willoughby Thomas Lake of the Magnificent and Captain Sir George Ralph Collier of the Medusa).
On 2 August General Gabriel de Mendizabal, the commander of the Spanish Seventh Army, in the north of Spain, arrived at Santander, with news that General Caffarelli, commander of the French Army of the North, was on his way towards Santander, and intended to try and rescue the garrison.
That news arrived just before the French escape attempt. On the night of 2-3 August Dubreton spiked the 18 guns in his works, and broke through the Allied siege lines to join Caffarelli. Caffarelli could have attempted to lift the siege, but he was aware that Wellington had just defeated Marmont at Salamanca (22 July 1812), and expected to be his next target. As a result he withdrew back to Vittoria, ready to defend his main base.
The conquest of Santander was Popham's most important achievement during this campaign. The port remained in Allied hands for the rest of the war. It became an important supply base during Wellington's failed siege of Burgos, but became even more important in 1813, when it became Wellington's main supply base during the successful Vitoria campaign.