In 1803, admiral Bruix summoned Magon to Boulogne to command the right wing of the flotilla for Napoleon's planned invasion of the United Kingdom. On 11 December 1803 he was made a member of the Légion-d'Honneur, rising to a commander in it on 14 June 1804. Napoleon ordered the flotilla to carry out an exercise and fleet review in the open sea. Magon considered this dangerous due to bad weather, but Bruix refused to excuse him from it. It proved a disaster as Magon had predicted, with a storm destroying 30 barges. In the months that followed Magon beat off several British attempts to destroy the flotilla.