Promoted to major-general, L'Estocq was stationed in New East Prussia in 1803, commanding all troops in the province as head of the 9th Hussar Regiment. In 1805 he was promoted to lieutenant-general. During the War of the Fourth Coalition, L'Estocq and his chief of staff, Gerhard von Scharnhorst, commanded some 15,000 troops based at Thorn in December 1806 and at Freystadt in January 1807. Harassed by Marshal Ney, L'Estocq marched his troops from February 2 - February 8 through snowy and forested East Prussia; it has been described as "a model of the way in which a flank march in the face of a near and powerful adversary should be conducted". The Russian troops of Bennigsen were hard-pressed by Marshal Davout in the Battle of Eylau. Leading the last operational unit in the Prussian army, L'Estocq was only able to bring eight battalions, twenty-eight squadrons, and two horse artillery batteries to the battle; the rest of his soldiers were defending against Ney. Upon the small Prussian contingent's arrival at Preußisch Eylau, Bennigsen wanted it split up to reinforce his weakened Russian troops. Scharnhorst, however, advised L'Estocq to strike with his cavalry around the Russian lines at Davout's exhausted troops; the sudden attack threw the French into disarray. Following the battle, L'Estocq's corps retreated to Preußisch Friedland to maintain coalition communications with Russia.
Honours
For their leadership in the battle, L'Estocq received the Order of the Black Eagle and Scharnhorst the Pour le Mérite. While the Prussian Army had been crushed at Jena-Auerstedt, L'Estocq's troops restored honor to the demoralized military. Colmar Freiherr von der Goltz wrote, "it was at Eylau in 1807, and not the War of Liberation in 1813, that the old army vindicated itself before the tribunal of history". Von der Goltz attributed the success to Scharnhorst's planning and L'Estocq's initiative and willingness to attack. After the coalition defeat in the Battle of Friedland and the humiliating Treaties of Tilsit, L'Estocq was part of an investigatory commission into the causes of Prussia's defeat in the Fourth Coalition. Because of his successful cooperation with L'Estocq, Scharnhorst successfully lobbied for attaching a chief of staff to each field commander in 1813. L'Estocq became Governor of Berlin on 12 November 1808, and of Breslau in 1814. After his death in Berlin on 5 January 1815, L'Estocq was buried in the cemetery of the city's garrison church three days later.
