Former US Marine Corps Hornet pilot Louis Gundlach takes an in-depth look at the ‘Night Killer’ of the Korean War, the Douglas F3D Skyknight.
In 1945, the U.S. Navy was alarmed that the Japanese air force was building jet-powered bombers and kamikaze aircraft. The Navy’s contemporary and planned propeller-driven fighters would be unable to intercept these extremely fast aircraft, especially at night. In response, the Navy put out a tender for a jet night-fighter that was to be equipped with an airborne intercept radar that could detect enemy aircraft out to 125 miles, an astonishingly demanding distance considering the then state-of-the-art. To put this into perspective, the detection of a small fighter out at 125 miles remains respectable in 2020! The Douglas Aircraft Company began work on a design built around the Westinghouse APQ-35 radar, which was actually a system made up of three radars. The main search radar, the APS-21, was equipped with a very large parabolic dish. This dish dictated that the nose of the aircraft would be very large. As well as being huge, the APQ-35 was also exceptionally complex and user intensive, so would require a dedicated Radio Operator. With these two design necessities in place, Douglas engineers designed a twin–engine aircraft with side-by-side seating. The aircraft became known as the F3D Skyknight.
The F3D-1 was equipped with two Westinghouse J-34 engines that each produced 3,400 pounds of thrust for a combined total of 6,800. While this was fairly good performance for a jet engine at that time, it wasn’t much grunt for an aircraft with a take-off weight of 25,414 pounds. The engines were also canted down, away from the aircraft, which further reduced the effective thrust of the engines. With the added drag of a large nose, two-place canopy, and large straight wings, the F3D was easily outperformed by the day fighters of the time. It first flew in 23 March 1948 and was in service by 1951.
It could climb to over 40,000 feet and reach a true airspeed of 500 knots at that altitude (around sixty knots slower than its day fighter contemporaries). The aircraft had combat radius of 500 nautical miles and with drop tanks added it had a radius of 590 nautical miles. It was armed with four 20mm cannon. The aircraft’s performance was less than ideal, but it was purposely built to be a night airborne interceptor.
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Like the Corsair in World War II and the Tigercat after the war, the Marine Corps came into possession of the Skyknight because of the type’s inability to operate from aircraft carriers. Though the F3D was found suitable for carrier operations, it would require a whole host of modifications to ensure safe operation onboard a carrier. Additionally, since the Navy had given the Marine Corps almost all of the radar-equipped Tigercats, the Navy did not have Radar Operators or a programme in place to train ROs. The APQ-35 was found difficult to operate and maintain, especially on the cramped confines of an aircraft carrier. The Navy also had not adopted new procedures for jet aircraft to operate from straight-deck carriers at night. Lastly, the F3D was a night interceptor only. It could not carry any bombs during its early years and the Navy was pushing for multi-role aircraft even back then. In the end, the U.S. Navy did not have the expertise to operate the radar, fix the radar, and operate the large Skyknight around the carrier at night, so they gave most of the F3Ds to the Marine Corps.
The F3D was built around the APQ-35 radar system. This radar had four functions: to search for airborne targets; to compute a gun solution for the 20mm cannon; to provide beacon interrogation and display beacon replies; and to provide a tail warning capability. As was mentioned, the APQ-35 was made up of three radars: The APS-21 was a long range search and intercept radar. It also supplied the beacon interrogation and display function; the APG-26 was a short-range gun aiming radar; the APS-28 was the tail warning radar. All three of these radars had separate radar dishes, transmitters, scopes, and controls. The APQ-35 had capabilities far exceeding other radars of the time, but it was nightmarishly laborious to use effectively.
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All of the controls for the three radars that made up the APQ-35 were found on the radar operator’s front console. Three scopes dominated the console along with various switches, knobs and buttons. The APS-21 radar was the primary search and intercept radar. The APS-21 had two dedicated radar displays dedicated to it. On the right side of the RO console there was a round C-scope which provided altitude and azimuth information to one contact. The primary scope for the APS-21 was a sector Plan Position Indicator (PPI) scope located on the left side of the RO console. The PPI provided range and azimuth indications on a display that was shaped like a third a piece of pie. The APS-21 had an elevation scan ability of -30 degrees below the horizon to +60 degrees above the horizon. Its azimuth search was up to 170 degrees and could locate fighter sized targets out to 40 nm. F3D ROs stated that the normal detection range for a fighter-sized target was around 18nm.
The APG-26 was a short-range gun aiming radar that could be used out to 4,000 yards. The APG-26 dish was located in front of the large APS-21 radar dish in the nose. The APG-26 radar scope was located on the right side of the pilot’s front console and was a C-scope. Controls for the APG-26 were located on the RO’s console. Range was provided via a dial beneath the scope that counted down from 2,000 yards. The target displayed on the scope was not a raw radar return, but a predicted target that was produced by the APG-26 ballistics computer. The APG-26 scope was round with vertical and horizontal cross hairs. The pilot would fly the target to the centre of the cross hairs and, when in range, could fire accurately without visually sighting the enemy aircraft.
The APS-28 was a rear warning radar and was based on the F4U-5N and the F7F-4N’s APS-19 radar. Controls for the radar were on the RO control panel along with its single scope. At the bottom of the scope were four red warning lights that would draw the RO’s attention to the scope in case a target was detected. The lights represented one quarter of the APS-28’s search area. The scope was an ‘H’ scope design that displayed two returns. The left return indicated azimuth and range, while the right return indicated altitude by referencing its position to the left return. It had a range out to four nautical miles and its operation was almost entirely autonomous.
Search and Intercept
The RO would use the APS-21 to search in front of the aircraft. While the F3D had exceptional radar capabilities for its time, it was still dependant on GCI radar. The radar would be set to search in 170 degrees azimuth with the range set at 80 nm. Elevation could be automatic, searching +60 degrees to – 30 degrees above and below the aircrafts nose position. Most ROs manually adjusted the elevation search using a 30 degree scan to search likely altitudes where enemy aircraft would be. The elevation control was a small switch which made accurate control difficult. The RO could also adjust the horizontal scan from 170 degrees to 30 degrees to look at a certain area. The only scope that would show airborne targets in search was the left PPI indicator. The PPI scope would show an airborne target that received a return from the transmitted radar energy.
Once a target was found on the radar that was to be intercepted, the RO would fine tune the radar to give more information on the target. The horizontal scan could be scaled down to 30 degrees to put more radar energy on the target. The RO would select the shortest range scale that would still have the target on the PPI. Then the RO would manipulate a range control knob to move a moveable range ring on the PPI scope. When the range ring intersected the desired target return, the target would then show up on the C scope. Once the range ring was over the target, accurate range was also displayed. If not already done, the RO would move the elevation scan to 30 degrees and centre the elevation around the contact on the C scope. Now the RO would begin to direct the pilot by directive then descriptive inter-cockpit communications. “Come left to 340 and climb, target bears 030, 25 miles, high” would be an example of the communications from the RO to the pilot. The RO could decipher basic heading and airspeed of the radar contact by the track the contact made across the PPI scope. There was not a set way to figure target heading and speed, only the RO’s experience and countless training runs would enable an educated guess. With help form the GCI controller, the F3D crew would manoeuvre the fighter to get behind the enemy contact at a desired range of about a mile and a half.
Once the aircraft closed to within 4,000 yards and the target is between 60 degrees horizontally and 30 degrees vertically from the nose and the range ring is over the target, a Gun Aim circle appeared on the C scope display. The RO could move the Gun Aim circle with the APG-26 radar controls to put the circle over the target return on the C scope. Once the Gun Aim circle was over the target return an On Target light illuminated and the target appeared on the pilot’s APG-26 gun scope. The RO could manually keep the Gun Aim circle over the target or he could actuate the lock button on his radar control panel. Once the lock button was pushed the APG-26 attempted to track the radar contact autonomously. With the target on the APG-26 scope, the pilot flew the target to the centre of the scope crosshairs. Inside of 2,000 meters, a range dial started to count down and the pilot could open fire inside 1,000 meters, with inside 500 meters being considered an effective range.
(Appendix 8 – APQ-35 airborne intercept interpretation.)
The Marine night fighter squadrons were excited to get the advanced F3D. When VMF(N)-542 left Korea, its aircrew, along with the aircrew of VMF(N)-531 received training in the Skyknight. Once they were done with their training, the aircrew, along with their F3Ds, were transferred to VMF(N)-513 located at Kunsan Airbase in Korea. VMF(N)-513 continued to operate as a composite night fighter squadron with the F3Ds operating along side the night Corsairs and Tigercats. The F3Ds initially had some maintenance problems and the Skyknight was grounded for a period of time in 1952. The Marine Pilots were anxious to try out the new jet fighter against the MiG-15s who had been operating at night since early 1951. The F3D would have been easy pickings for the MiG in the day time, but with its advanced radar, the aircrew felt the Skyknight was more than a match for the MiG-15 at night.
Initially the F3Ds operated in a similar fashion to the F4U-5N and the F7Fs. CAP positions were picked near the front lines in hopes of intercepting a communist night bomber or a MiG heading south. During the first couple months of action the Skyknights did not intercept any enemy aircraft and the aircrew had thought the air war had passed them by. During this time, the U.S. Air Force B-29s began to run into serious opposition at nigh due to MiG-15 intercepting them on their bombs runs into North Korea. The B-29s were restricted from flying in the day time because the MiGs had exacted a heavy toll on the bombers during daylight raids. The MiGs were beginning to have effects on the unescorted bombers at night. The U.S. Air Force’s night fighter, the F-94B was thought to be too valuable to fall into enemy hands and was restricted to South Korea. This left VMF(N)-513 and their F3Ds to provide cover for the bombers.
The F3Ds developed tactics to escort the B-29s that differed from the tactics used by the U.S. Air Force in World War II. The new tactics enabled the RO to work the radar and run an intercept away from the bombers. Coordination would start at the brief were on station times, frequencies, headings to and from the target, and the likely threat was briefed. Most of the squadrons F3Ds would be airborne to support these missions. If enough aircraft were available, a couple of F3Ds would launch as airborne spares, in case a primary aircraft had a maintenance problem. If unneeded, the spares would often set up a CAP to intercept communist night bombers. Other F3Ds would provide escort for the bombers, as well as a high and low barrier cap, and a target CAP. These missions would used in the future, with attached and detached escort, BARCAPs, and TARCAPS being standard missions flown by fighter pilots in the future
Two F3Ds would normally comprise the escort. These aircraft would operate a single aircraft and would be separated by altitude and range. The Skyknights would use their radar to intercept the bombers as they entered into enemy airspace. From the intercept, the night fighters join up with the bomber formations. The F3Ds would offset toward one side of the bombers as the fighters flew along side the formation. With the offset, the APS-21 would paint the bomber stream and a threat could be picked up trying to fly toward the bombers. These F3Ds would fly with the bombers until they reached the target area. At that point another two F3Ds would pick up the bombers and escort them out of enemy territory. These F3Ds would sometimes have part of the bomber formation within visual range along the route but mostly the bomber formations position was known by using the radar. This would become known as a detached escort. If the fighters were alerted by GCI that an enemy aircraft was closing, the F3D could leave the formation and intercept the enemy fighter.
Usually four other F3Ds would set up a barrier CAP on the south side of the Yalu River. Two of the jets would set up and orbit at around 15,000 feet and the other two would fly around 30,000 feet. These caps would form a barrier between the bomber formation and the MiG bases located in China. The CAPs would run in a racetrack type pattern that usually was 40 nm in length. The ends of the two cap positions were usually separated by 10 miles. The high cap could expect to experience the most action, as friendly GCI had trouble seeing the MiGs below 15,000 feet across the Chinese border. GCI would direct the fighters to intercept the MiGs as they crossed the border because the allied fighters could not fly into Chinese territory. The low cap could expect to pick up the contact on the APS-21 search radar and run an intercept without the help of GCI.
A single aircraft, usually manned by the most experience aircrew would orbit near the target area. The “target” cap would set up between the target and the threat sector. The F3D would position itself to intercept any MiGs attempting to attack the bombers in the target area. This F3D aircrew would also act as an airborne commander, making tactical decisions in relation to the other F3Ds airborne. If an F3D was experiencing radar problems, the target cap aircrew might direct an airborne spare to take its place. He might also move fighters into new positions in light of enemy movements.
(Appendix 9 – F3D escort of B-29 formation.)
The F3Ds quickly scored kills on the Communist fighters. The B-29s offered the bait for the enemy fighters to come up and the day fighters could not compete, at first, with the F3Ds sophisticated radar system. The first kill came on 3 November, 1952, with a barrier low cap aircraft intercepting a communist jet fighter.
On 3 November, 1952 at approximately 0107/I (Korea local time) at 14,000 feet, contact was made on radar. Unidentified at same altitude, heading approximately 330 degrees, speed 320 knots. Distance 7 miles. Contact lost, then again established, same distance. Closed to 2,100 feet. APG-26 [gun aiming radar] would not lock [and] visual sighting [was] made of single-engine jet-type aircraft identified as Yak-15 at 0110. After some delay, permission was give by Dutchboy [allied GCI] to “Bag Bandit.” Opened fire at approximately 0113 at 12,000 feet altitude. 1,200 feet from directly astern. First burst hit port wing of bands, second fuselage, third entered tailpipe, exploding therein. Three explosions in all were observed and plane smoke heavily as it went down. Last seen at 6,000 feet still on fire and smoking.
The kill was the first night kill between two jets in aviation history. The actual identification of the enemy fighter is doubted because the Yak-15 was not widely produced or used. It was possibly a follow-on Yak fighter, the Yak-23, which was reportedly seen by other allied pilots over Korea. After achieving MiG kills escorting the B-29s in the early winter of 1952/53, the MiGs changed tactics and began to target the Marine F3Ds. The communist GCI also showed signs of improvement during this time. Lastly the communists started to jam the night fighter communications with GCI. A tactic that was observed by the F3D crews during this time was one MiG would act as “bait” and fly in front of the F3D and another set of MiGs would climb from low altitude to attack the Skyknight which was distracted intercepting the “bait” MiG. During this time the Chinese would jam the F3D communications which kept friendly GCI from warning the F3D crew. If it was not for the APS-28 tail warning radar, a couple of Skyknights would have undoubtedly been lost to this bait tactic.
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