 The plan was launched on 7 July 1810 as two combined forces of British sailors , soldiers , sepoys and Royal Marines landed at separate beaches . Although a number of men were drowned in the heavy surf , the majority of the invasion force reached the beaches safely and marched inland , attacking French outposts as they approached the capital . Recognising that his demoralised garrison would be unable to defend Saint Denis and that the militia would take too long to mobilise , the French commander Colonel <unk> de Sainte @-@ Suzanne surrendered the island , its garrison and its stores to Rowley . 
