<P> On the eastern front, progress was very slow . The Russian army was heavily dependent upon its main magazines in Poland, and the Prussian army launched several successful raids against them . One of them, led by general Platen in September resulted in the loss of 2,000 Russians, mostly captured, and the destruction of 5,000 wagons . Deprived of men, the Prussians had to resort to this new sort of warfare, raiding, to delay the advance of their enemies . Nonetheless, at the end of the year, they suffered two critical setbacks . The Russians under Zakhar Chernyshev and Pyotr Rumyantsev stormed Kolberg in Pomerania, while the Austrians captured Schweidnitz . The loss of Kolberg cost Prussia its last port on the Baltic Sea . A major problem for the Russians throughout the war had always been their weak logistics, which prevented their generals from following up their victories, and now with the fall of Kolberg, the Russians could at long last supply their armies in Central Europe via the sea . The fact that the Russians could now supply their armies over the sea, which was considerably faster and safer (Prussian cavalry could not intercept Russian ships in the Baltic) than over the land threatened to swing the balance of power decisively against Prussia . In Britain, it was speculated that a total Prussian collapse was now imminent . </P> <P> Britain now threatened to withdraw its subsidies if Prussia did not consider offering concessions to secure peace . As the Prussian armies had dwindled to just 60,000 men and with Berlin itself about to come under siege, Frederick's survival was severely threatened . Then on 5 January 1762 the Russian Empress Elizabeth died . Her Prussophile successor, Peter III, at once ended the Russian occupation of East Prussia and Pomerania (see: the Treaty of Saint Petersburg (1762)) and mediated Frederick's truce with Sweden . He also placed a corps of his own troops under Frederick's command . Frederick was then able to muster a larger army, of 120,000 men, and concentrate it against Austria . He drove them from much of Silesia, while his brother Henry won a victory in Saxony in the Battle of Freiberg (29 October 1762). At the same time, his Brunswick allies captured the key town of Göttingen and compounded this by taking Cassel . </P> <P> 1762 brought two new countries into the war . Britain declared war against Spain on 4 January 1762; Spain reacted by issuing their own declaration of war against Britain on 18 January . Portugal followed by joining the war on Britain's side . Spain, aided by the French, launched an invasion of Portugal and succeeded in capturing Almeida . The arrival of British reinforcements stalled a further Spanish advance, and the Battle of Valencia de Alcántara saw British - Portuguese forces overrun a major Spanish supply base . The invaders were stopped on the heights in front of Abrantes (called the pass to Lisbon) where the Anglo - Portuguese were entrenched . Eventually the Anglo - Portuguese army, aided by guerrillas and practicing a scorched earth strategy, chased the greatly reduced Franco - Spanish army back to Spain, recovering almost all the lost towns, among them the Spanish headquarters in Castelo Branco full of wounded and sick that had been left behind . </P> <P> Meanwhile, the long British naval blockade of French ports had sapped the morale of the French populace . Morale declined further when news of defeat in the Battle of Signal Hill in Newfoundland reached Paris . </P>

What did both britain and france do as a result of the seven years' war