The river assault of the 5th RCT was only lightly opposed. The Marines were mounted in LVTs (Landing Vehicles Tracked), literally amphibious armored personal carriers. These vehicles and crews were provided by the Marine 1st Amphibious Tractor Battalion, and the US Army’s 56th Amphibious Tractor Company. In addition, some Marines at Inchon and at the crossing of the Han River rode in army DUKW amphibious trucks of the 1st Amphibious Truck Company. Importantly, X Corps had no assault-bridging capability, so they could not put a military bridge over the Han. This meant that it was very time-consuming to move the important M-26 tanks of the 1st Marine Tank Battalion across the river to support the 5th RCT. Finally, as the plan was fashioned, four RCTs would participate in the battle of Seoul, each attacking in a set sequence. The sequencing of these attacks was all determined by the requirement that all four RCTs be moved across the river by the same single LVT battalion. Thus, the Han River obstacle shaped the assault on Seoul more than any other single factor.
The intent of the attack of the 5th RCT was to get behind the defenses of Seoul as the assumption was that the North Korean forces would be oriented south and southwest towards the approaches directly from Inchon. What the planners of the operation failed to account for was that the area northwest of Seoul was a former Japanese army training area, and had been improved by the South Korean army as a defensive line, so the positions were oriented north against attack from North Korea. Those prepared defensive positions were still in place and the North Korean army occupied them in defense against the attack of the 5th RCT. In addition, the North Korean army moved approximately 10,000 troops into these positions just prior to the Marines crossing the Han. Thus, though the 5th RCT covered 4 miles on the afternoon of river crossing, September 20, it then ran into stiff resistance. It would take the Marines five more days to fight their way across the last four miles of ridges between their landing site and Seoul.
On September 24, the 1st RCT crossed the river, assaulting directly from Yongdungpo into the heart of the city. With three battalions abreast, the 1st RCT attacked directly east through a series of roadblock barricades that the North Koreans had constructed on the major thoroughfares through the city. The 5th RCT wheeled left, and advanced on the left flank of the 1st RCT as both Marine units systematically cleared barricades, buildings, culverts, and sewers. Both regiments used their M-26 Pershing tanks extensively. Typically a single tank led a Marine infantry platoon as it systematically cleared the interiors of the buildings. The Marine tanks were virtually unstoppable, and easily brushed aside North Korean infantry, and also made short work of a few Soviet-built T-34/85 tanks found in the city.
On September 25, two additional regiments entered the battle for Seoul. One was the 32nd Infantry Regiment of the US Army’s 7th Infantry Division. The other was the 1st ROK Infantry Regiment, attached to the 7th Infantry Division. These two regiments, using the same LVTs as the 1st and 5th RCTs, crossed the Han River into the southern part of Seoul. Thus by September 25, the four allied regiments were on line advancing across Seoul. On the night of September 25–26, the North Korean army mounted a last major counterattack against the 5th, 1st, and 32nd Regiments. The attack against the 1st Marines was led by T-34 tanks and self-propelled assault guns. In the morning the two Marine regiments counted almost 500 enemy dead as well as nine destroyed armored vehicles and eight antitank guns in front of their positions. The steady advance of the three major regiments, supported by the 17th ROK Army Regiment, continued on September 26, and on September 27 the major portion of the city was cleared of communist forces and the X Corps lead elements were pursuing the enemy north through the mountains toward the 38th parallel. It had required 12 days for the X Corps to achieve its objective after landing at Inchon.
The only other major combat formation involved in the battle for Seoul was the 7th Marine Regiment of the 1st Marine Division. This regiment was still en route to Korea when the initial Inchon landings occurred. It landed at Inchon on September 21. The 7th Marines’ role in the Seoul operation was to isolate the city and prevent North Korean forces from escaping the city to the northeast. As the 5th Marines attacked into the city from the north the 7th Marines passed behind them and attacked east. Unfortunately, the direction of attack to the east was across numerous valleys divided by very rugged mountains aligned north to south, and the area was virtually unsupported by roads. Thus, though not strongly opposed, the attack proceeded very slowly. It was only on September 28 that the northeast escape routes were closed, and by then some of the best North Korean troops defending Seoul had escaped.
On September 29, 1950, General Douglas MacArthur and South Korean president, Syngman Rhee, arrived in the capital and General MacArthur declared the city secure. In fact, significant fighting continued as the American units in the city, aided by South Korean forces, continued to systematically clear buildings and streets. Nonetheless, the city was declared secured exactly 90 days after the outbreak of hostilities. The major portion of the 1st Marine Division moved to the eastern portion of the city and prepared to pursue the North Korean army north. Earlier, on September 26, at Suwon, 30 miles south of Seoul, elements of the US Eighth Army linked up with X Corps’ 7th Infantry Division. Between Seoul and Pusan, the North Korean army was completely shattered.
A Fluid Battle
Large urban areas are very difficult objectives to seize except at great cost both in resources and time. The key to the successful capture of a large city, quickly and with minimum expenditure of resources, is to seize it before it is adequately defended. This is extremely difficult to do and can only be accomplished through one of three types of operations: airborne assault; amphibious attack; or a deep rapid armored thrust. General MacArthur recognized that a counteroffensive launched from the Pusan perimeter alone would likely devolve into a long and costly battle of attrition through the Korean mountains, and through numerous large urban areas, including Seoul. The Inchon landing operation, at some significant risk, avoided a war of attrition and resulted in the fall of Seoul in just over 10 days with minimum losses. Unlike most World War II urban battles, the battle for Inchon and Seoul was a battle of maneuver. This was primarily because the attacking force was able to achieve strategic surprise and thus the defender did not have the time to assemble forces and could not establish a comprehensive defense of the entire city area.
The US Marine approach to urban warfare in Seoul was relatively straightforward. Seoul was a huge city which, with Yongdungpo, covered about 80km2 (30 square miles). Despite having more than 20,000 troops available, the North Korean Army had insufficient manpower to defend a continuous line of buildings. The North Korean forces in the city choose to defend fortified barricades oriented on the major avenues and significant natural and city terrain features. The fight for the city became known as the battle of the barricades. Along the city streets the North Korean army erected barricades, constructed of whatever material the North Koreans could find within the city. This included rubble and dirt-packed rice bags, bricks, household furniture, old cars and buses, and any other obstacle-making device they could find. These were torn down by the US and ROK infantry and engineers, or driven over by US tanks. The Marines developed a standard approach to the barricades: artillery fire on the area followed by mortar fire on the position; machine-gun and bazooka fire to suppress the enemy while engineers cleared mines; and finally with the mines removed, the tanks moved forward. The powerful US M-26 tanks were often able to simply plow through the assorted debris. With the tanks came the Marine infantry armed with semiautomatic rifles, fixed bayonets, and grenades. Marine scout-sniper teams overwatched all operations and took a deadly toll on any enemy not behind cover. Each barricade was stoutly defended by North Korean infantry supported by antitank guns, machine guns, and snipers; and took about 45 to 60 minutes to reduce. Thus the movement through the metropolis was of necessity slow, but steady.