The rangers left him in command of a detachment, in possession of the fort at Cap au Gris.[11] Soon after the main body of the rangers had marched away, the fort was besieged by a body of English and Indians. The besiegers made several attempts to storm the fort, but were repelled by the garrison.--The foe continued the siege for a week, continually firing upon the garrison, who sometimes, though not often, for want of ammunition, returned the fire. Lieutenant Pattie, perceiving no disposition in the enemy to withdraw, and discovering that his ammunition was almost entirely exhausted, deemed it necessary to send a despatch to Bellefontaine,[12] near the point of the junction of the Missouri and Mississippi, where was stationed a considerable American force. He proposed to his command, that a couple of men should make their way through the enemy, cross the Mississippi, and apprize the commander of Bellefontaine of their condition. No one was found willing to risk the attempt, as the besiegers were encamped entirely around them. Leaving Thomas McNair[13] in command in his place, and putting on the uniform of one of the English soldiers, whom they had killed during one of the attempts to storm the fort, he passed by night safely through the camp of the enemy, and arrived at the point of his destination, a distance of over forty miles: 500 soldiers were immediately dispatched from Bellefontaine to the relief of the besieged at Cap au Gris. As soon as this force reached the fort, the British and Indians decamped, not, however, without leaving many of their lifeless companions behind them.
Lieutenant Pattie remained in command of Cap au Gris, being essentially instrumental in repressing the incursions of the Sacs and Foxes, and disposing them to a treaty of peace, until the close of the war.[14] In 1813 he received his discharge, and returned to his family, with whom he enjoyed domestic happiness in privacy and repose for some years. St. Louis and St. Charles { x} were beginning rapidly to improve; American families were constantly immigrating to these towns. The timber in their vicinity is not of the best kind for building. Pine could no where be obtained in abundance, nearer than on the Gasconade, a stream that enters on the south side of the Missouri, about one hundred and fifty miles up that river. Mr. Pattie, possessing a wandering and adventurous spirit, meditated the idea of removing to this frontier and unpeopled river, to erect Mills upon it, and send down pine lumber in rafts to St. Louis, and the adjoining country. He carried his plan into operation, and erected a Saw and Grist Mill upon the Gasconade.[15] It proved a very fortunate speculation, as there was an immediate demand at St. Louis and St. Charles for all the plank the mill could supply.