Operation Thunderbolt, also known in China as the Defensive Battle of the Han River Southern Bank (), was a US offensive during the Korean War. It was the first offensive under the new commanding officer of the US Eighth Army, General Matthew Ridgway and started less than three weeks after the Chinese Third Phase Campaign had forced UN forces south of Seoul.
Operation Wolfhound On 15 January 1951 Ridgway ordered a reconnaissance in force by US I Corps. Ridgway warned I Corps' commander General Frank W. Milburn against permitting any situation to develop during the operation that would require additional forces to extricate those initially committed. Neither was Milburn to attempt a large scale exploitation, if that opportunity occurred, except on Ridgway's order. If all went according to instructions, Ridgway estimated, the operation would be concluded by dark on the 15th or, at the latest, on the 16th. Milburn assigned the main task to the 25th Infantry Division, instructing General William B. Kean to attack the Suwon-Osan area with an infantry regiment and a battalion of tanks supported by artillery and engineers. Kean selected as the central force the 27th Infantry Regiment Wolfhounds, from whose nickname the reconnaissance was named Operation Wolfhound. To protect the main force on the east, Milburn ordered the 3rd Infantry Division to send a smaller force of infantry and tanks to cut the Suwon-Kumnyangjang-ni stretch of the lateral Route 20 and instructed the Republic of Korea Army (ROKA) 1st Infantry Division to send a battalion as far as Ch'on-ni (), on Route 17 south of Kumnyangjang-ni (). Ridgway notified U.S. IX Corps also to provide protection on the east, for which IX Corps' commander General John B. Coulter directed the ROKA 6th Infantry Division to station a battalion in blocking positions just east of Kumnyangjang-ni.
On the 15th the ROKA battalions reached Ch'on-ni and Kumnyangjang-ni over Route 17 without contact. The 1st Battalion, 15th Infantry Regiment, and two companies of tanks from the 3rd Division which followed the same axis to Kumnyangjang-ni received small arms and heavy mortar fire after turning west for on Route 20 toward Suwon. An exchange of fire with some 6-800 PVA held the 3rd Division force in place for the remainder of the day. Wolfhound forces elsewhere met no opposition, but were delayed by damaged roads and bridges. The bulk of the reinforced 27th Infantry moving over Route 1 in the main effort halted for the night at the northern edge of Osan. The 1st Battalion of the regiment and tanks following Route 39 near the coast stopped at Paranjang, to the west.
As Colonel John H. Michaelis' two columns converged on Suwon over Routes 1 and 39 on the morning of the 16th, Milburn ordered the Wolfhound forces to withdraw to the Chinwi River at 14:00. Having so far met only a few PVA, who appeared to be stragglers, Michaelis ordered a motorized company of infantry and a company of tanks from each column to sprint ahead and inflict as much damage as possible on enemy forces discovered in Suwon before withdrawing. On the left, after the tank-infantry team moving on Route 39 to Route 20 and then turning east came to a destroyed bridge southwest of Suwon, dismounted infantry continued the advance and investigated the southwestern edge of town without finding PVA/KPA forces. On Route 1 the tanks and infantry received fire from a strong PVA force deployed south of Suwon and from machine gunners atop buildings inside town. Michaelis' team deployed and returned the fire for a half hour, then under the cover of air strikes withdrew out of range.
The Wolfhound forces developed a Corps' outpost line along the Chinwi with a westward extension to the coast and pushed patrols back into PVA/KPA territory. Ridgway commended them, more for the offensive spirit displayed than for results achieved. Milburn estimated that the two-day operation had inflicted 1,380 PVA/KPA casualties, 1,180 by air strikes, five captured and 195 killed by ground troops, his own losses were three killed and seven wounded. The PVA captives identified three armies, but since the 27th Infantry had taken these prisoners before running into the PVA position at Suwon, the identity of the unit defending the town was obscure. Most pertinent, the reconnaissance revealed that no large force was located south of the Suwon-Kumnyangjang-ni line, but that organized groups did hold positions along it.
Having successfully concluded Wolfhound on 20 January, Ridgway instructed his Corps' commanders to devise similar operations. Milburn responded on the 22nd with an infantry-armor strike built around the 35th Infantry Regiment that in concept nearly duplicated Operation Wolfhound. Two small encounters during the one-day operation resulted in three PVA/KPA killed and one captured with no losses to the regiment. The strike confirmed the absence of strong PVA/KPA forces within of the I Corps front. It also raised the possibility that KPA forces were now operating south of Seoul when the captive identified his unit as the 8th Division, part of KPA I Corps.
Task Force Johnson During the week before Ridgway issued his 20 January directive he had prodded Coulter to increase the strength, continuity, and depth of IX Corps’ reconnaissance. He also had directed Coulter to move the 1st Cavalry Division's 70th Tank Battalion from its deep reserve location near Sangju in the Naktong River valley to Chinch'on, behind the Corps front. From Chinch'on the tankers were to back up the ROKA 6th Infantry Division and also were to be employed in a reconnaissance in force wherever Coulter saw an opportunity. Regardless of Ridgway's dissatisfaction, Coulter was certain that his patrols had shown the IX Corps sector below the Kumnyangjang-ni-Ich’on-Yoju road to be free of any large PVA/KPA force. Since 12 January the 24th Infantry Division had kept a battalion in Yoju, and on the 21st General John H. Church dispatched another battalion accompanied by tanks and a battery of artillery to Ich'on with instructions to stay until pushed out. At the Corps' left, the ROKA 6th Infantry Division had not established outposts that far forward but had placed a battalion at Paengam-ni on secondary Route 55, short of the Kumnyangjang-ni-Ich'on stretch of Route 20.
After receiving Ridgway's instructions on the 20th, Coulter scheduled for the 22nd a one-day operation built around the 70th Tank Battalion in which his force was to push north of Route 20 between Kumnyangjang-ni and Ich'on. The 1st Cavalry Division was to mount the operation, developing and pushing the PVA/KPA in the objective area without becoming heavily engaged. General Hobart R. Gay organized a task force under the 8th Cavalry Regiment commanded by Colonel Harold K. Johnson that added infantry, artillery, and engineers to the tank battalion. Johnson was to move up Route 55 through the South Korean outpost at Paengam-ni to Yangji-ri on Route 20, then investigate east and west along the road and the high ground immediately above it. Johnson's principal engagement was an exchange of fire with an enemy company discovered on the reverse slopes of the first heights above Yangji-ri. The task force suffered two killed and five wounded, while enemy casualties were estimated at 15 killed by ground troops and 50 by air strikes. The lack of contact before reaching Yangji-ri supported Coulter's conviction that the area below Route 20 was unoccupied, while the Yangji-ri exchange supplied further evidence that organized enemy groups were located along the road.
Operation Reconnaissance in force (9-29 January) Ridgway wanted a clearer picture of PVA/KPA dispositions below the Han River before committing forces to general offensive operations. On 23 January his intelligence officer reported the bulk of the PVA XIII Army Group to be below Seoul in the area bounded by Route 20 on the south and the Han River on the east and north. Air reconnaissance had been reporting steady troop movements below the Han but did not confirm the presence of such a large force in that region. Nor had recent ground contacts developed any solid enemy defense at the area's lower edge. Resolving the ambiguities, Ridgway judged, required a deeper and stronger reconnaissance in force, which he scheduled for the morning of the 25th under the name Operation Thunderbolt.
In the operation Milburn and Coulter were to reconnoiter as far as the Han, each using not more than one US division reinforced by armor and, at the discretion of each Corps commander, one South Korean regiment. Each Corps' force was to establish a base of operations on the night of the 24th along a line of departure ahead of Line D, from the coast through Osan to Yoju, then advance to the Han in multiple columns through five phase lines about apart. To ensure a fully coordinated reconnaissance, Ridgway made Milburn responsible for ordering the advance from each phase line in both Corps' zones; to guarantee the security of the advance, he instructed Milburn to order each successive move only after he had clearly determined that no enemy group strong enough to endanger any column had been bypassed. Ridgway intended that his ground troops would have ample air support. He planned to postpone the operation if for any reason on the 25th Fifth Air Force commander General Earle E. Partridge could not assure two successive days of maximum close support. Ridgway also arranged for I Corps to be able to call down gunfire from a heavy cruiser and two destroyers of Task Force 95 stationed off Inchon.
X Corps was to protect the right flank of the Thunderbolt advance. On 23 January Ridgway had his deputy chief of staff, Brigadier general Henry I. Hodes, deliver instructions to General Edward Almond requiring X Corps to maintain contact with IX Corps at Yoju and to prevent enemy movements south of the Yoju-Wonju road. Almond, as he had been instructed three days earlier, also was to send forces in diversionary forays north of this road.
On the 24th Ridgway reconnoitered the objective area from the air with Partridge as his pilot. The two generals flew low over the territory ahead of the I and IX Corps fronts for two hours, but saw no indications of large enemy formations. Although this flight did not conclusively disprove the current intelligence estimate, Ridgway was more confident that his forces would reach the Han, and he also saw possibility of holding the ground covered. That night, from a forward command post established at I Corps headquarters in Cheonan, he ordered Milburn and Coulter to prepare plans for holding their gains once their forces achieved the fifth phase line stretching eastward from Inchon. The two Corps' commanders completed these plans on the 25th. Thus the Thunderbolt reconnaissance tentatively assumed the nature of a general attack within a few hours after it started.