The landing forces consisted of about 650 men (over 500 sailors and 100 Marines). In this fight, the US had Remington rolling block carbines (.50-45), the Marines had Springfield muskets and Navy Plymouths; the Koreans had matchlocks. They landed at Choji Fortress on June 10, with no opposition; they camped nearby overnight. The next morning, they finished destroying the fort, dumping or spiking cannons and then moved on, with Marines travelling ahead as skirmishers.
The Korean forces banded together as guerilla units but, armed with only matchlocks, and being kept in check by US artillery (12-pdr. howitzers on field carriages), they could not get within effective firing range. The US troops moved on toward the next objective, Dukjin Fortress (Fort Monocacy).
The Korean forces had, likewise, abandoned the second fortress, choosing to mass together farther north. The Marines quickly dismantled this fortress, too. Like the past fortress, they dumped and spiked cannon, burned stores, etc.
Next, they went onward toward their main objective, Kwangsungbo (Citadel). The Korean forces had regrouped there, en masse. Along the way, some Korean units tried to flank the US forces; they were checked, again, by strategic placement of artillery on two hills nearby the Citadel.
Artillery, both from the ground forces and also from the USS Monocacy, offshore, pounded the Citadel and the hill directly west of it, in preparation for an assault by US forces. The US forces, made up of nine companies of sailors and one company of Marines, grouped on the facing hill, keeping cover and firing at any defender who showed himself.
When a signal was given, firing stopped and the US forces charged toward the Citadel, with Lt. Hugh McKee in the lead. The Koreans fired as fast as they could, but the US forces gained ground before they could reload; the Koreans even ended up throwing rocks at the attackers. Lt. McKee was the first in the Citadel, with a sword in one hand and a revolver in the other. He was shot in the groin and speared in the side by Koreans inside. After him came Commander Schley, who shot and killed the Korean who speared Lt. McKee.
The fighting went on for only fifteen minutes or so and all the defenders were either killed, wounded and captured or escaped. When the fighting was over, about 350 Koreans were dead and three Americans (Lt. McKee, landsman Seth Allen and Marine Denis Hanrahan).
The US won the battle, militarily, but lost diplomatically, as the Koreans refused to open up the country to them (and the US forces didn't have authority or strength for occupation); within a couple weeks, the US fleet left Korean waters.
The next US military presence in Korea took place at the end of WWII, in 1945; the next military conflict in Korea, involving the US, was the 1950-53 Korean War.