He took a small frigate squadron flying false British colours to Killala, and in August landed 1,150 French troops under General Humbert. A larger force would have been despatched, but the French had been caught unprepared—the Irish rebellion had originally been planned to coincide with a later French landing, but British intelligence operations had infiltrated the United Irishmen and arrested much of its leadership, prompting a precipitate revolt. Although the uprising achieved some early successes, by the time Humbert arrived its outcome had already been decided with the defeat of successive rebel armies by British troops. Humbert's force was joined by many United Irishmen and had some initial success, but was unable to face superior British numbers at the Battle of Ballinamuck, and surrendered on 8 September. Although its small size allowed it to reach Ireland unobserved, neither Savary's frigate squadron nor the army it carried were large enough to have a significant impact on the campaign. Unaware that Humbert had surrendered and the rebellion been defeated, the French prepared a follow-up expedition under the command of Commodore Jean-Baptiste-François Bompart. Three thousand men were embarked aboard the ship of the line "Hoche" and eight frigates, the force departing Brest on 16 September. However, having missed Savary's frigate squadron, the Royal Navy were more watchful; roving frigate patrols cruised off the principal French ports and in the approaches to Ireland, while squadrons of battleships from the Channel Fleet sailed nearby, ready to move against any new invasion force. In command of the squadron on the Irish station was Commodore Sir John Borlase Warren, a highly experienced officer (and politician) who had made a name for himself raiding the French coast early in the war. Bompart's squadron departed Brest late in the evening, hoping to slip past the inshore British blockade in the dark. However, they took too long to navigate the Raz passage, and were spotted at dawn on 17 September by a frigate squadron under Captain Richard Goodwin Keats, in HMS "Boadicea". Keats immediately divided his forces, ordering HMS "Ethalion" under Captain George Countess and the brig HMS "Sylph" under Commander John Chambers White to follow the French force, while Keats brought news of the French movements to Admiral Lord Bridport, admiral of the Channel Fleet. Aware of the British pursuit, Bompart nevertheless continued to the north. Countess followed closely, and was joined on 18 September by HMS "Amelia" under Captain Charles Herbert.