Doggedly pursued by the French under Soult, the British made a retreat across northern Spain while their rearguard fought off repeated French attacks. Both armies suffered extremely from the harsh winter conditions. Much of the British army, excluding the elite Light Brigade under Robert Craufurd, suffered from a loss of order and discipline during the retreat. When the British eventually reached the port of Corunna on the northern coast of Galicia in Spain, a few days ahead of the French, they found their transport ships had not arrived. The fleet arrived after a couple of days and the British were in the midst of embarking when the French forces reached them. They forced the British to fight another battle before being able to depart for England.
In the resulting action, the British repulsed the French assault and completed their embarkation. They saved their army from destruction. But the port cities of Corunna and Ferrol, as well as northern Spain, were captured and occupied by the French. During the battle, Sir John Moore, the British commander, was mortally wounded, dying after learning that his men had repulsed the French attacks.
In early October 1808, following the scandal in Britain over the Convention of Sintra and the recall of the generals Dalrymple, Burrard and Wellesley, Sir John Moore took command of the 30,000-man British force in Portugal. In addition, Sir David Baird in command of an expedition of reinforcements out of Falmouth consisting of 150 transports carrying between 12,000 and 13,000 men, convoyed by HMS Louie, Amelia and Champion, entered Corunna Harbour on the 13 October. By November 1808 the British army, led by Moore, advanced into Spain with orders to assist the Spanish armies in their struggle against the invading forces of Napoleon.
After the surrender of a French army corps at Bailén and the loss of Portugal, Napoleon was convinced of the peril he faced in Spain. Deeply disturbed by news of Sintra, the Emperor remarked,
I see that everybody has lost their head since the infamous capitulation of Bailén. I realise that I must go there myself to get the machine working again.
The French, all but masters of Spain in June, stood with their backs to the Pyrenees, clutching at Navarre and Catalonia. They did not know if even these two footholds could be maintained in the face of a Spanish attack. By October French strength in Spain, including garrisons, was about 75,000 soldiers. They were facing 86,000 Spanish troops with Spain's 35,000 British allies en route.
However, no attack came. The Spanish social fabric, shaken by the shock of rebellion, gave way to crippling social and political tensions; the patriots stood divided on every question and their nascent war effort suffered accordingly. With the fall of the monarchy, constitutional power devolved to local juntas. These institutions interfered with the army and the business of war, undermined the tentative central government taking shape in Madrid, and in some cases proved almost as dangerous to each other as to the French.[b] The British Army in Portugal, meanwhile, was itself immobilized by logistical problems and bogged down in administrative disputes, and did not budge.
Months of inaction had passed at the front, the revolution having "temporarily crippled Patriot Spain at the very moment when decisive action could have changed the whole course of the war". While the allies inched forward, a vast consolidation of bodies and bayonets from the far reaches of the French Empire brought 100,000 veterans of the Grande Armée into Spain, led in person by Napoleon and his Marshals. With his Armée d'Espagne of 278,670 men drawn up on the Ebro, facing a scant 80,000 raw, disorganized Spanish troops, the Emperor announced to the Spanish deputies:
I am here with the soldiers who conquered at Austerlitz, at Jena, at Eylau. Who can withstand them? Certainly not your wretched Spanish troops who do not know how to fight. I shall conquer Spain in two months and acquire the rights of a conqueror.
Starting in October 1808 Napoleon led the French on a brilliant offensive involving a massive double envelopment of the Spanish lines. The attack began in November and has been described as "an avalanche of fire and steel".
For a time the British army was dangerously dispersed, with Baird's newly arrived contingent at Astorga to the north, Moore at Salamanca and Hope 70 miles (110 km) to the east near Madrid with all Moore's cavalry and artillery. The main army, under Moore, had advanced to Salamanca and were joined by Hope's detachment on 3 December when Moore received news that the Spanish forces had suffered several defeats. He considered that to avoid disaster he must give up and retreat back to Portugal.[c]
Moore, before retreating, received intelligence of Soult's 16,000 man corps' scattered and isolated position at Carrión and that the French were unaware of the British army's position. On 15 December, he seized this opportunity to advance on the French near Madrid, hoping that to defeat Soult and possibly divert Napoleon’s forces. A junction with Baird on 20 December, advancing from Corunna, raised Moore's strength to 23,500 infantry, 2,400 cavalry and 60 guns and he opened his attack with a successful raid by Lieutenant-GeneralPaget's cavalry on the French picquets at Sahagún on 21 December. However, Moore failed to follow up against a surprised Soult. Moore halted for two days and allowed Soult to concentrate his corps.