He was afterward employed to make a survey of the environs of (p. 026) Philadelphia, which was to be the seat of the approaching campaign, to take soundings in the Delaware, and to fortify Billingsport. (_Certified by General Washington_). The enemy having landed at Hith, he joined the army and acted as major of brigade. At the battle of the Brandywine, he remained on the field after his brigade had been routed, had a horse shot under him, and carried off a piece of ordnance. On the report of General Washington to Congress, it was ordered that a horse be presented to M. de Fleury "as a mark of the high sense Congress entertained of his merits." (_Certified by General Washington and General Sullivan_). N.B. This honour has been paid only to General Arnold and M. de Fleury. At the battle of Germantown he acted as brigade-major of dragoons, charged several times, and made several prisoners. The horse which had been given to him by Congress was shot under him, and he himself was wounded in the leg. (_Certified by General Count Pulaski_). Fort Mifflin, on Mud Island, the only defence of the Delaware, was threatened by the British army and squadron. It was a post of the greatest importance, and M. de Fleury was sent there as chief engineer. He sustained a siege of six weeks behind a stockade. A ship of sixty-four guns, the Augusta, and one of 22 guns, the Merlin, blew up under fire from the fort. The commandant and the garrison, numbering 600 men, were relieved three times, but M. de Fleury refused to leave the fort. He was wounded October 15th, and the fort was evacuated that same night. For this action he was made a lieutenant-colonel, and a letter of thanks was addressed to him by the President of Congress. (_Certified by Congress, the General-in-chief, and M. de la Fayette_). During the winter of 1778 he formed the project of crossing the ice and setting fire to the English squadron. The Delaware not being frozen that year hard enough for his purpose, he invented explosive boats, and he was engaged in constructing them when he received orders to join the Army of the North. (_Certified by General Washington and Commodore Hasilwood_). The Canadian expedition did not take place, and on his return M. de Fleury was appointed inspector and charged with forming, instructing, and disciplining the troops. (_Certified by General Washington_). At the opening of the campaign of 1778 he was second in command of a select corps (in which was the general's body-guard) of 600 men, 2 pieces of ordnance, and 50 cavalry. He served in this capacity at the battle of Monmouth and afterward.