The supply routes from the Chinese depots to the front lines consisted of a railroad system and a road network, much of it primitive and unimproved. The railroads were a primary objective of the UN air campaign in Korea. During the winter of 1951–52, the majority of strike sorties from TF 77 were directed against the railroad system. Priority targets were the locomotives, then the rolling stock, followed by bridges and then the tracks themselves.
After some initial successes by TF 77 aircraft against operating locomotives, referred to as “loco busting,” the North Koreans, whenever possible, kept their trains in long, deep mountain tunnels by day and moved them only at night. Occasionally during a night mission, an F4U-4N or AD-1N would immobilize a locomotive in an open area by rockets or strafing, and the next day a large-scale commitment of sorties from the Task Force 77 carriers would be scheduled in an all-out effort to destroy the engine in daylight precision attacks by Skyraiders and Corsairs with heavy bombs. The Communists quickly countered by moving in batteries of 37mm automatic weapons and heavy machine guns on flatbed cars along the tracks adjacent to the stalled locomotive. This didn’t deter the carrier strikes, but the missions became more complicated, with jets added for flak suppression, attacking the antiaircraft cars with 20mm automatic cannons, rockets, and 260-pound frag bombs. This increased level of effort diverted sorties from other tactical missions and resulted in a sharp increase in friendly losses. Nevertheless, a stalled locomotive was a big event, relished by the pilots as an exciting target to be destroyed with skillfully coordinated tactics. It was much more satisfying than cutting rails.
In the dedicated campaign to interdict the railroad system, lucrative targets soon became scarce. Tunnels proved effective in protecting the trains. Squadrons developed various tactics to toss bombs inside the tunnels, such as skip bombing. A 1,000-pound bomb with delayed fusing was released at minimum altitude over the track leading into the tunnel. The 1,000-pounder would hit the tracks with a flat trajectory, skip into the tunnel entrance, and explode deep inside. There were many problems with this tactic, however. There had to be a straight run of track leading into the tunnel, and there had to be maneuvering room for the attacking plane, usually an AD, to make the low-level approach and pull up after release to get over the mountain through which the tunnel penetrated. In pursuing these tactics, planes were lost, crashing into the terrain during the approach and postdelivery recovery. On occasions when this tactic was successful, the results were said to be spectacular. The detonating bomb was, in effect, an exploding cartridge blowing everything in the tube of the tunnel out the far end like the muzzle of a gun. The North Koreans emplaced heavy automatic weapons along the tracks at the tunnel approaches, however, so the flat, low-level skipbombing approach finally became lethal for the attacking aircraft.
Railroad bridges were prime targets in the interdiction effort. Early in the campaign most of the substantial concrete and steel spans were knocked out by major carrier deckload strikes. The North Koreans rebuilt those bridges that were on the MSR and surrounded the sites with flak positions in depth and in a variety of calibers.
ARMED RECONNAISSANCE
The most important interdiction missions flown by Task Force 77 jets were armed reconnaissance missions covering the road networks in Northern Korea. Because of the speed and agility of the jets, virtually all of the route recces were conducted by Panthers. Most of these lines of communications (LOCs) and MSRs were one-lane dirt-and-gravel roads that wound through the valleys and mountain passes of the rugged mountainous territory that made up most of North Korea. The curves and slopes in these roads limited the ahead visibility of low-flying aircraft to no more than a couple of miles. The mountainous terrain made armed reconnaissance missions especially tricky and often difficult, because the aircraft usually could not see potential targets until the last minute. On the other hand, those on the ground could not see approaching aircraft until they were virtually overhead. If the aircraft overran the target, the pilot could circle and attack on the second pass. On the mountain roads, the trucks usually had nowhere to go but over a precipice.
In the flat coastal plain areas of Korea such as Hungnam and Wonsan, vehicle movement along the MSR was visible for miles and consequently vulnerable to artillery and naval gunfire. So the Communists avoided moving any traffic along these exposed routes except at night or during low visibility. But those routes that wound through the mountains could only be reconnoitered by aircraft and then only attacked effectively by air. The defilade of the terrain prevented artillery or naval gunfire interdiction.
During the final two years of the war, with the Communists and UN forces engaged across the relatively static east-west front, route recces, along with railroad interdiction, became especially relied upon to slow the flow of logistics and combat consumables to the enemy’s combatant troops. Normally each carrier jet squadron would be scheduled for two road recce missions each flying day. A mission consisted of four jets armed with six HVAR rockets or four 260-pound frag bombs and full 20mm ammunition. All of the main roads comprising the LOCs and MSRs in North Korea were organized into numbered recce routes by the JOC. Each designated route consisted of an MSR segment of fifty to seventy-five miles. This was the maximum distance that could be covered by a division of jets, as flying at low altitudes and high speed with external munitions resulted in high rates of fuel consumption.
The tactical formation for road recces was unique for that mission had evolved with experience. Different squadrons employed variations of the basic techniques. After launch, the four planes would join up in a standard two section close tactical formation and cross the beach at ten thousand feet, checking in with the TAC. At the initial point of the route, the jets would make a rapid letdown from ten thousand feet with the pilots moving into the recce formation. The lead plane would descend to three hundred feet above the road. Initially the airspeed would be about 300 knots, but with the weaving and turning to stay over the road, airspeed was soon reduced to about 250 knots. The number two pilot maintained an altitude of about one thousand feet above and on the quarter of the low jet. Pilots three and four maintained a loose-section formation three thousand feet higher, where they could provide air cover against MiGs and keep a lookout ahead to assist in navigation and warn of flak.
The number one pilot served as the spotter. At his low altitude he could discern whether an object in the road was an ox cart, truck, or military vehicle and whether it was active or abandoned. As he flew over the object, the spotter would call out his evaluation, such as, “Over a truck now, attack with rockets” or “Over an abandoned ox cart, no target.” The number two pilot at one thousand feet would be watching the low plane’s position closely and at the spotter’s call would know exactly where to look for the target. Then from his perch position he could select and arm his weapons and make a precision attack. If bombs were used, a minimum pullout altitude of five hundred feet was required to avoid bomb blast. With rockets, a flat run could be made, firing as close in as fifty yards followed by a sharp pull-up. The 5-inch HVAR was powerful enough to cause blast fragment damage to the firing aircraft unless a sharp breakaway was made. This use of a spotter plane on the deck and the attacker at one thousand feet allowed a precision attack with any weapon without having to circle around to gain position for the attack.