Here they were for some time blockaded by the British Channel Squadron under Lord Gambier, whose flag was flying on board the _Caledonia_, of 120 guns, Captain Sir H. Burrard Neale. Lord Gambier had himself suggested the possibility of destroying the French fleet by means of fire-ships, though he considered, as his letter expresses it, "a horrible mode of warfare, and the attempt very hazardous, if not desperate." The Admiralty had, however, anticipated him, and had already ordered the construction of several fire-ships, which, on the arrival from the Mediterranean of Lord Cochrane, commanding the 38-gun frigate _Imperieuse_, were placed under his command. On his reaching the fleet he was coldly received by the other captains, who were jealous of the appointment of a junior officer to conduct so important a service. Lord Cochrane remarks that two only, Rear-Admiral Stafford and Sir Harry Neale, received him in a friendly manner. Lord Cochrane was not a man to be disconcerted by such conduct, and felt thoroughly convinced that the plan he proposed would succeed. The French, aware of the danger of their position, had done their utmost to fortify it. The defences on Ile d'Aix were strengthened, and works were commenced on the Boyart Shoal on the opposite side of the entrance to the roads, while a boom half-a-mile in length, composed of spars and cables, had been laid down and secured by heavy anchors. This boom, forming an obtuse angle, occupied a deep channel between Ile d'Aix and the Boyart Shoal, and it was supposed would prove effectual against the passage of fire-ships. The French fleet was drawn up in two lines inside the boom, with three frigates in line ahead of them. The ships thus placed, aided by the batteries on shore, would have been sufficient to sink the British fleet had it attempted to force a passage. Besides the fire-ships, Lord Cochrane had constructed two explosion vessels. The largest contained 1500 barrels of powder, formed into a solid mass by wedges and wet sand rammed hard between the casks. On the top of this mass of gunpowder were 400 live shells with short fusees, together with as many hundreds of hand grenades and rockets.