As
Operation Ripper showed that the PVA/KPA forces were withdrawing north of Seoul, US
Eighth Army commander General
Matthew Ridgway planned to block and attack the retreat of KPA
I Corps. On 21 March Ridgway ordered US I Corps to move forward to the
Cairo Line, which he extended southwestward across General
Frank W. Milburn's zone through
Uijongbu () to the vicinity of Haengju () on the Han River. At points generally along this line to the north, Milburn's patrols had made some contact with KPA I Corps west of Uijongbu and the PVA
26th Army to the east. Milburn was to occupy the
Cairo Line on 22 March, a day ahead of the airborne landing at
Munsan-ni, and wait for Ridgway's further order to continue north. Requiring Milburn to wait stemmed from Ridgway's not yet having given the final green light to the airborne landing,
Operation Tomahawk, as of 21 March. Operation Tomahawk would take place only if Ridgway received assurances that weather conditions on 23 March would favor a parachute drop, and that ground troops could link up with the airborne force within twenty-four hours. If these assurances were forthcoming, the
187th Airborne Regimental Combat Team (187th RCT), with the
2nd and
4th Ranger Companies attached, was to drop in the Munsan-ni area on the morning of 23 March and block
Route 1. Milburn was to establish physical contact with and assume control of the airborne force once it was on the ground. At the same time, he was to open a general Corps' advance toward the
Aspen Line, which traced the lower bank of the Imjin River west and north of Munsan-ni, then sloped eastward across the corps zone to cut Routes 33 and 3 north of Uijongbu. Once on
Aspen, Milburn was to expect Ridgway's order to continue to the
Benton Line, the final Courageous objective line, some farther north. Reaching
Benton would carry I Corps virtually to the
38th Parallel except in the west where the final line fell off to the southwest along the Imjin. Because I Corps otherwise would have an open east flank when it moved to the
Benton Line, Ridgway extended its line southeastward into the US
IX Corps' zone, across the front of the 24th Division and about halfway across the front of the ROK
6th Infantry Division to a juncture with the
Cairo Line. When Ridgway ordered I Corps to
Benton, General
William M. Hoge was to send his western forces to the line to protect the I Corps' flank. Meanwhile, in concert with Milburn's drive to the
Cairo and
Aspen Lines, General Hoge was to complete the occupation of his sector of the
Cairo Line. Elsewhere along the army front, US
X Corps and the ROK
III and I Corps remained under Ridgway's order of 18 March to reconnoiter the area between the
Hwach'on Reservoir and the east coast. As yet, neither General
Edward Almond's patrols nor those of the ROK corps had moved that deeply into North Korean territory. The three divisions of I Corps started towards the
Cairo Line at 08:00 on 22 March. The ROK
1st Infantry Division, advancing astride Route 1 in the west, overcame very light resistance and had troops on the phase line by noon. The ROK
3rd Infantry Division astride Route 3 in the center and the US 25th Infantry Division on the right also met sporadic opposition, but moved slowly and ended the day considerably short of the line. Meanwhile, Milburn assembled an armored task force in Seoul for a drive up Route 1 to make the initial contact with the 187th RCT, if and after it dropped on Munsan-ni. Building the force around the 6th Medium Tank Battalion, which was borrowed from the
24th Infantry Division of IX Corps, he added the
2nd Battalion, 7th Infantry Regiment; all but one battery of the 58th Armored Field Artillery Battalion from the 3rd Division; and from Corps' troops he supplied a battery of the 999th Armored Field Artillery Battalion and Company A,
14th Engineer Combat Battalion. He also included two bridgelaying
Churchill tanks from the British
29th Brigade, which had recently been attached to I Corps. Lt. Col. John S. Growdon, commander of the 6th Medium Tank Battalion, was to lead the task force. Ridgway made the final decision on the airborne operation late in the afternoon of 22 March during a conference at Eighth Army main headquarters in
Taegu. General
Earle E. Partridge, the
Fifth Air Force commander, assured him that the weather would be satisfactory on the next day; Colonel
Gilman C. Mudgett, the new Eighth Army
G-3 operations officer, predicted that contact with the airborne unit would be made within a day's time, as Ridgway required, and also that the entire I Corps should be able to advance rapidly. Given these reports, Ridgway ordered the airborne landing to take place at 09:00 on the following day. On hearing the final word on the Munsan-ni drop, Milburn directed
Task Force Growdon to pass through the ROK 1st Division on the
Cairo Line early on 23 March and proceed via Route 1 to reach the airborne troops, while his three divisions were to resume their advance with the objective of reaching the
Aspen Line. The ROK 1st Division, which would be following
Task Force Growdon, was to relieve the 187th RCT upon reaching Munsan-ni, and the airborne unit then was to prepare to move south and revert to Eighth Army reserve. ==First attack==