The invasion was planned by the Duc de Choiseul who became French foreign minister in December 1758 and effectively served as Prime Minister during the period of the mooted invasion. He wanted to launch a bold initiative that would knock Britain out of the war with one stroke. French pride had been stung the previous year by the ease with which the British had captured Louisbourg and launched amphibious raids on the French coast during 1758, such as that against Cherbourg. British financial subsidies and military aid to her only ally Prussia had kept that country afloat since 1756. Choiseul's brief as foreign minister was to overturn this situation.