It was decided, and Brown was soon thoroughly familiar with the fort, which was about one hundred feet square and located on a small hill near the northeast bank of the St. Illa River, which he learned was defended by seventy men, mostly Georgia recruits but including more than a dozen Continental regulars who were thought to be well trained and competent. Captain Winn was young, but obviously eager to make a name for himself. His instructions were to limit forays outside the fort and to concentrate on self-defense. Maintaining a permanent military presence so far south in Georgia was, in itself, an important symbolic victory.

Brown imposed a close observation on the activities of the fort, and also in Savannah within the Continental command. There was no real attempt to conceal intelligence either within the military offices or in the taverns where officers and men gathered to drink and exchange rumors and information. He was soon rewarded with a report that food and ammunition would be delivered to Fort McIntosh by barge, down the inland waterway and up the St. Illa River to the fort.

Brown decided that he would let Sergeant Baker and Lieutenant McGirth lead the expedition, while he stayed behind in St. Augustine. Their plan was to intercept the shipment at the mouth of the river, replace the crew and escort troops with Rangers, and take the fort after the gates were opened to receive the much-needed supplies. A force of about ninety men would be deployed close enough to surround the fort at the crucial time and ensure that the operation was successful.

A courier informed the Ranger commander as soon as the shipment left Savannah on the slow-moving barge, and the plan was put into effect. It was implemented without a hitch, and the fort was taken with minimal loss of life on either side. As was customary, Captain Winn and the other captured defenders were released on their personal guarantee of no further military service, but McGirth insisted that Lieutenant Christie be taken captive to St. Augustine as a guarantor that the noncombatant pledges would be honored. Two experienced Tory volunteers and four Creek braves guarded the prisoner. There was confusion among the group as they crossed the St. Marys River, and Christie was killed as—according to his captors—he attempted to escape. Before the white Rangers could restrain them, the Creeks scalped the dead Georgian, and after a brief discussion, his body was buried near the river.