Observing the French fleet's departure from the harbour at dusk, Pellew immediately dispatched Phoebe to Colpoys and Amazon to the main fleet at Portsmouth with warnings, before approaching the entrance to Brest in Indefatigable with the intention of disrupting French movements.[8] Believing that the frigates in the bay must be the forerunners of a larger British force, de Galles attempted to pass his fleet through the Raz de Sein. This channel was a narrow, rocky and dangerous passage, and de Galles used corvettes as temporary light ships that shone blue lights and fired fireworks to direct his main fleet through the passage.[3] Pellew observed this, and sailed Indefatigable right through the French fleet, launching rockets and shining lights seemingly at random. This succeeded in confusing the French officers, causing the Séduisant to strike the Grand Stevenent rock and sink with the loss of over 680 men from a complement of 1,300.[9] Séduisant's distress flares added to the confusion and delayed the fleet's passage until dawn.[8] His task of observing the enemy completed, Pellew took his remaining squadron to Falmouth, sent a report to the Admiralty by semaphore telegraph, and refitted his ships.[3]