Amphibious Warfare: Cold War Era

1950 - UN landing at Inchon (Operation CHROMITE) turns tide of Korean War

In the summer of 1950, the commander-in-chief of U.S. forces in the Far East, General Douglas MacArthur, faced a daunting challenge. North Korean forces had poured across the border with South Korea in June 1950. They had overrun one defensive barrier after another, driving U.S. and South Korean forces into a tight perimeter around the port of Pusan on the southeastern tip of the peninsula. Consequently, MacArthur's most immediate task was to maintain this last foothold of U.S. and allied forces in Korea.

The general did not plan on holding this position by remaining on the defensive. Looking ahead, he envisioned a near-simultaneous amphibious landing in the rear of the enemy formations in South Korea, and a counteroffensive by reinforced forces within the Pusan perimeter. The amphibious assault was the key to the scheme - MacArthur wanted a major landing on South Korea's west coast, at a point from which U.S. forces could sever the lines of communication between the North Korean People's Army (NKPA) and their homeland.

The general considered Inchon, a port approximately 25 miles west of the South Korean capital of Seoul, the best place for this assault. Rail and road nets in South Korea converged on the area around Inchon and the capital, making it a key logistics and communication node for NKPA forces. With this in mind, MacArthur ordered his staff to begin planning for Operation Chromite, an amphibious assault at Inchon, on 12 August 1950. The staff of Rear Admiral James Doyle, commander of the four-ship, Far East-based Amphibious Group One, a group of 57 Marines from Landing Force Training Center, Pacific, and personnel from a Tactical Air Control Squadron initiated the planning effort for Chromite. During the next month, these and other U.S. planners around the world would have to deal with an array of obstacles.

Building an Amphibious Force

The first of these obstacles was where to find sufficient forces. MacArthur had initially considered putting an Army cavalry division ashore as part of a relatively unopposed "administrative" landing. Events intervened, however - the Army division was inserted into Pusan - leading MacArthur to request a Marine division to conduct an opposed landing into the Inchon area.

On paper, Chromite called for an initial landing by a 20,000-man Marine division, along with 4,000-man Marine air wing. Logically, this requirement would be filled by the west coast-based 1st Marine Division and 1 Marine Aircraft Wing. However, after its post-World War II demobilization and subsequent budget cuts, the strength of the entire active Fleet Marine Force was only 28,000. Moreover, the 1st Marine Division, which was already undermanned before the war began, had already dispatched one brigade to the Pusan perimeter that July.

Bringing the division up to strength would require the movement of units from around the world and the activation of the Marine Reserve (which President Harry Truman authorized in July 1950). Marine Corps commanders were finally able to cobble together an entire division by transferring a brigade from the 2nd Marine Division on the East Coast, fleshing out other units with mobilized Reservists and non-Fleet Marine Force personnel, and calling upon a Battalion Landing Team then afloat in the Mediterranean near Crete. They also were able to retrieve the Marine brigade fighting in the Pusan perimeter in the weeks before the assault - but not without fierce protests from the hard-pressed U.S. Army commander defending that pocket. The commanding general of the 1st Marine Division, Major General Oliver P. Smith, also was named the landing force commander.

MacArthur's plan called for a two-division landing at Inchon, meaning that the 1st Marine Division had to be supported by a follow-on force. The unit chosen to do this was the Army's Far East-based 7th Infantry Division, which had been cannibalized during the initial rush of U.S. forces to Korea and then brought back up to strength - on paper, at least - by more than 8,000 South Korean recruits. Once the Marine and Army divisions were established ashore, they would fall under the command of X Corps, led by MacArthur's chief of staff, General Edward M. Almond. In turn, X Corps and its component divisions, at least initially, would be part of Joint Task Force 7, headed by Admiral Arthur D. Struble, commander of the U.S. 7th Fleet. JTF 7's overall objectives were to land at and seize Inchon, capture Kimpo airfield on the outskirts of Seoul and the capital itself, and then seal off NKPA lines of communication running through the area.

In addition to the two divisions, Admiral Struble had more than 230 ships to help him achieve the JTF's objectives. Approximately 20 percent of the ships belonged to screening and support forces, which included fast carrier, patrol and reconnaissance, and logistics task groups. The attack force carrying X Corps to the objective area consisted of 120 amphibious transports, accompanied by another 60 escorts, gunfire support ships, minesweepers, and other supporting vessels.

Hundreds of Navy and Marine Corps aircraft were available to support Chromite. Two Marine squadrons flying from a pair of escort carriers would provide direct support to the assault, adding their ordnance to surface fires from two heavy cruisers, two British light cruisers, eight destroyers, and two rocket-launching landing assault craft. Meanwhile, Navy aircraft from offshore fast carriers would attack targets in the wider area around Inchon. In the absence of nearby land bases, Air Force participation would be minimal.

Landing Site Problems

As the forces that would carry out Chromite moved toward the theater and the command structure for the operation fell into place, detailed planning continued. However, much of the broader plan was already in place by the time important players such as General Smith reached the theater - it had to be, given the situation on the ground and the vagaries of Inchon's hydrographic conditions as well as constricted geography.

From an operational perspective, Inchon was the perfect place for an amphibious assault, but from a practical perspective there could be few worse places to launch an attack from the sea. The amphibious task force and supporting warships would face a long, narrow channel with little maneuvering room; strong 7-8 knot currents; and large tidal fluctuations - much as the Rodgers expedition had almost eighty years earlier. The tides essentially dictated the timing and character of the operation - 15-18 September would be the only time that month that the high tide would allow critical landing ship, tank (LST) transports and other amphibious craft to ride over the broad mudflats off Inchon and deliver critically needed equipment and supplies to the beach. Hence, 15 September became D-Day for Operation Chromite.

Map showing the approaches to Inchon, August - September 1950

The approaches to Inchon, August - September 1950.  From James A. Field, Jr, History of United States Naval Operations: Korea (1962); Naval Historical Center.

In addition, even during this the acceptable period, the tide was only high enough for a two short periods during the day, near dawn and twilight. Given the lack of time and sea maneuvering room, strong currents that hindered the movements of amphibious shipping, and the absence of any real beaches in the Inchon area, planners decided that the assault itself would have to occur in two waves separated by both time and space. During the first assault in the morning, a Marine battalion landing team would seize Wolmi-do Island, a small landmass topped by a peak that commands the seaborne approaches to Inchon. The island is connected to the city itself by a causeway.

During the second landing, which would be conducted near twilight on D-Day, the remainder of the 1st Marine Division would come ashore on beaches to the north and south of Wolmi-do. With the tide ebbing, LSTs run ashore at the northernmost beach would have to unload their entire cargo quickly, or remain stranded on the mudflats until the next high tide - they could not leave the Marines without key pieces of combat equipment. Moreover, all of these useful transports (many of which were manned by Japanese crews) would beach themselves while Marine units were moving through the city only hundreds of yards inland.

Intelligence Shortfalls

Much of the Chromite plan had been put together in the absence of detailed, on-the-ground intelligence. U.S. planners in the Far East believed that the bulk of the NKPA was arrayed around Pusan and that Inchon was not heavily garrisoned, beliefs that were validated during the subsequent operation. However, given that the U.S. and Japanese charts of the Inchon area varied widely, they were forced to rely on aerial reconnaissance and the recollections of individuals who had operated in the Inchon area in the aftermath of World War II. A small group of intelligence collectors was also placed ashore two weeks prior to D-Day.

Another unknown in these relatively early years of the Cold War concerned the possibility of Soviet or Chinese intervention. MacArthur developed his plans on the assumption that the Soviets and Chinese would not intervene directly, another belief borne out by later events. However, the Soviet Navy was providing a form of indirect aid to North Korea that potentially had major implications for the success of the Inchon assault. Russian advisors and mines - including both contact and magnetic mines, the latter particularly difficult to counter - were already being sent to Korean ports, including Inchon. U.S. intelligence efforts did not detect the magnitude of these efforts, and thus planners assumed that mines would not be a significant problem during Chromite. While this turned out to be correct, it was the result of other factors. 

Fire Support and Surprise

Fire support was yet another area of uncertainty. World War II operations had demonstrated the importance of thorough pre-assault bombardment. However, U.S. commanders did not want to draw unnecessary attention to the Inchon area by concentrating air and surface attacks against the city and its environs. They ultimately decided to begin a preliminary bombardment two days before the landing. Until that time, carrier-based Navy and Marine aircraft would also strike the area, but only in conjunction with surface and air attacks on other points along the east and west coast of Korea where amphibious assaults might conceivably occur.

Deception was a key part of the overall Chromite plan, given the relatively open build-up of U.S. forces and shipping in Japan. Air strikes, bombardment by surface warships, feints by special operations forces, and the spread of disinformation in Pusan (where North Korean spies were present) all served to draw attention away from the prospective landing at Inchon.

Weather

Weather was an important wild card in the Inchon operation. On 3 September, Typhoon Jane struck Japan, damaging ships and interfering with the loading of amphibious shipping for the assault. Later that month, meteorologists predicted that Typhoon Kezia would pass through the Tsushima Strait between Japan and Korea on 12 or 13 September - just as the amphibious task force was passing through the area - and head into the Yellow Sea off Korea's western coast. Taking a calculated gamble that the storm's track would curve to the east, Admiral Struble ordered the amphibious task force to sortie a day early. The storm ultimately did cooperate by moving east, missing the area in which the task force was steaming. Had Kezia swung into the Yellow Sea, the September Inchon assault may never have been attempted.

These were just some of the myriad obstacles that U.S. forces had to overcome in the 34 days between General MacArthur's announcement of his plan for Operation Chromite and the assault itself. This compressed period left little time for activities such as ensuring the optimal combat loading of the amphibious task force's transports, and no time for rehearsals. Moreover, key players met for the first time in the weeks or days preceding - or in the case of General Smith's staff, the days after - the assault itself.

Executing Chromite

Despite this short time frame and the complexity of the operation, Chromite was executed essentially as planned. The first Marines came ashore on Wolmi-do early on the morning of the 15 September 1950, an hour after the first air strikes had rocked the port area and 45 minutes after naval gunfire and rockets had swept the landing areas. The island itself was secured by noon and supporting fires shifted inland.

Photo of first wave of Marines heading ashore at Inchon, 15 September 1950

The first wave of Marines heads ashore at Inchon, 15 September 1950.  Naval Historical Center.

The second round of landings began late that afternoon, after another intense air and surface bombardment. Marines clambered over the seawalls that surrounded the city's industrial and port facilities, encountering only moderate opposition from the approximately 2000-man garrison spread throughout the area around Inchon. By midnight, the landing force had reached its initial objectives. During the next two days, more supplies and men poured ashore, well ahead of X Corps forecasts. The first 7th Infantry Division regiment came ashore on D+3, followed soon after by the remaining two.

Photo of an LMSR bombarding Wolmi-do Island

A rocket-firing medium landing ship (LMSR) bombards Wolmi-do Island
as landing craft head for the beach. Naval Historical Center.

Meanwhile, the 1st Marine Division advanced on Seoul, facing counterattacks from NKPA troops hastily deployed for North Korea proper. Kimpo Airfield fell two days after the initial landing; four days later Marine aircraft were operating from the field. By 21 September Marine units were on the outskirts of the capital facing increasingly heavy resistance. Six days later Seoul was secure.

At the operational level, the amphibious turning movement at Inchon had the effect that MacArthur had foreseen. Coalition forces in the Pusan perimeter at first faced undiminished resistance as they attempted to break out of their encirclement, but NKPA resistance progressively weakened in the days after the invasion. Finally, 10 days after the Inchon assault, the NKPA's initial retreat turned into a general collapse.

Map depicting the rollback of North Korean forces after the Inchon landing, September 1950

Map depicting the rollback of North Korean forces after the Inchon landing, September 1950.
From James A. Field, Jr, Field, History of United States Naval Operations: Korea (1962); Naval Historical Center.

Overall, U.S. forces prevailed at Inchon despite several serious threats, both from North Korean forces and the environment. The presence of modern sea mines and well-placed minefields, or uncooperative weather could have stymied the entire operation. Nevertheless, Marine Corps and Navy planners pressed forward, building and employing an effective force in a minimal amount of time. Only extensive training; common, well-understood amphibious doctrine; and prior experience with amphibious warfare allowed them to do so.

By any standard, Inchon represented a remarkable effort by U.S. naval forces facing enormous odds. As General MacArthur signaled Admiral Struble from his flagship on 15 September, as Marines streamed ashore on Wolmi-do, "The Navy and Marines have never shone more brightly than this morning.“

Sources:

James A. Field, Jr., History of United States Naval Operations: Korea (Washington, DC: Government Printing Office, 1962).

Colonel Robert D. Heinl, Jr., USMC (ret.), "Inchon, 1950" in Lieutenant Colonel Merrill L. Bartlett, USMC (ret.), ed., Assault from the Sea (Annapolis, MD: Naval Institute Press, 1983).

Colonel Robert D. Heinl, "The Inchon Landing: A Case Study in Amphibious Planning, Naval War College Review, May 1967, reprinted Spring 1998.

Allan R. Millett, Semper Fidelis: A History of the United States Marine Corps (New York: The Free Press, 1991).

Back to Top