At the outset of the war, Frederick had one of the finest armies in Europe: his troops—any company—could fire at least four volleys a minute, and some of them could fire five. By the end of 1757, the course of the war had gone well for Prussia, and poorly for Austria. Prussia had achieve spectacular victories at Rossbach and Leuthen and reconquered parts of Silesia that had fallen back to Austria. The Prussians then pressed south into Austrian Moravia. In April 1758, Prussia and Britain concluded the Anglo-Prussian Convention in which the British committed to pay Frederick an annual subsidy of £670,000. Britain also dispatched 7,000–9,000 troops to reinforce Frederick's brother-in-law, the Duke Ferdinand of Brunswick-Wolfenbüttel's army. Ferdinand evicted the French from Hanover and Westphalia and re-captured the port of Emden in March 1758; he crossed the Rhine, causing general alarm in France. Despite Ferdinand's victory over the French at the Battle of Krefeld and the brief occupation of Düsseldorf, successful maneuvering of larger French forces required him to withdraw across the Rhine.