Lessons from Vietnam: Guns and Sustained Turns
The F-15 Eagle was designed in December 1969 to replace the McDonnell Douglas F-4 Phantom II. Experiencing serious problems highlighted from air combat seen in the Vietnam War, the United States Air Force (USAF) sought to procure a fighter aircraft with more effective radar and weapon systems, albeit with similar or even higher speed and longer combat radius than the F-4. This move was met with much controversy, owing to a series of flaws in the F-4’s design and projected combat performance. There was stiff opposition from a group of USAF officers and aerial warfare analysts called the Fighter Mafia, which was primarily led by John Boyd and Pierre Sprey. They argued that the Air Force should use a dedicated fighter weighing less than 9.1 metric tons (20,000 lb), without any provisions for ground attack or even the use of technologically-advanced radar. This became the Light-Weight Fighter (LWF) program, which would result in the General Dynamics F-16 Fighting Falcon in 1974. To understand the significance of this, it helps to look at the doctrine and actual performance of USAF F-4 fighters in Vietnam.
In the decades immediately following World War II, the USAF employed the doctrine of using jets chiefly as interceptor aircraft, where the primary mission was to eliminate enemy bombers and attack aircraft before they could threaten friendly surface units. The priority targets being Soviet strategic bombers armed with nuclear munitions. The Air Force was of the opinion that missiles, namely the AIM-9 Sidewinder and AIM-7 Sparrow, had made the use of guns obsolete, and that their premier fighter need not feature such a weapon. They felt that dogfighting was a thing of the past, and focused on fielding a fighter with impressive long range, high-speed capabilities. However, the reality of fighters engaging in dogfights was very real, as they would later find out. USAF top brass had failed to consider the inherent value that such a high-volume weapon, like that of a rotary gun, provides in a close range, sustained turning fight. Their doctrine was absolutely dependent on radar tracking and missile seeker capabilities, which to many pilots’ dismay and frustration, did not live up to expectations at the time. Most of the AIM-7 semi-active radar-guided missiles launched in the Vietnam War failed to track their targets or even start their motors due to the tropical conditions, rendering them useless entirely. According to Barry D. Watts in his study Six Decades of Guided Munitions and Battle Networks, only 97 of the 612 AIM-7 (D, E and E-2 variants) missiles fired managed to hit their targets.
In line with USAF’s aerial warfare doctrine of sortieing high-speed, long range interceptors, the Phantom II was designed from the outset to employ air-to-air missiles be a Fleet Air Defence fighter for the US Navy in 1960, then later adopted as a fighter-bomber by other branches of the US military, namely the Air Force and Marine Corps. The main design drawbacks that the F-4 had were its sub-par sustained turn ability due to its relatively large mass, and the lack of an internally-mounted gun, exacerbating its performance in subsonic dogfights. This put the Phantom at a significant disadvantage when engaging smaller and more agile MiG-17, MiG-19 and MiG-21 fighters for the most part of the War. These second- and early third-generation MiGs often outperformed the less agile F-4s in Within Visual Range (WVR) engagements, using auto-cannons and their superior maneuverability to their advantage. The Phantom’s saving grace was its superior thrust, which enabled it to out-climb and rapidly disengage its opponents. To address the lack of a close range, high-saturation weapon, the USAF introduced the SUU-16 external gun pod on the F-4E variant, which housed an M61 Vulcan 20x102mm rotary cannon. The SUU-16 gun pod was mounted under the fuselage, giving the F-4E a slight edge in close range engagements. That said, the SUU-16 was not without its problems. The external gun pod increased drag on the F-4E’s airframe, along with the added weight of the rotary gun and the ammunition it used. Furthermore, many of the M61 Vulcans were inaccurately sighted in, resulting in pilots having a hard time landing their rounds on enemy aircraft.
Rising Tensions and the Iron Curtain
At the time, the Cold War (mainly between the Soviet Union and the United States) was reaching boiling point, with Saigon (capital of South Vietnam) falling into Communist rule. The Soviets had gathered intelligence on the USAF’s experimental XB-70 Valkyrie high-supersonic strategic bomber, when one of the prototypes crashed in June 1966. Realising that the Americans had the technology to develop a strategic bomber capable of penetrating their airspace at an unbelievable 3,300km/h (Mach 3.1), the Soviet designers at Mikoyan-and-Gurevich (MiG) quickly developed an interceptor based on the Valkyrie’s features. The resulting aircraft was the MiG-25 Foxbat, constructed using titanium, and capable of rivaling the XB-70’s speed and altitude. The Foxbat was revealed to public for the first time in 1966 as a state-of-the-art fighter during a Soviet military parade. The USAF pushed for a new fighter that could counter this new threat, and McDonnell Douglas was eager to improve upon its F-4 Phantom II.
The Eagle is Born
With advancements in computer technology, McDonnell Douglas went back to the drawing board. Engineers made use of more efficient and effective radar, coupled with a lightweight composite airframe and an internally-mounted M61, developed the F-15 Eagle in July 1972. The F-15A initial production model was a single-seat, highly-maneuverable fighter jet capable of reaching speeds up to 2,700km/h at high altitude. It also holds the distinction of being the only known USAF fighter to ever successfully launch an anti-satellite missile, the ASM-135 ASAT. The F-15A, along with the F-15B tandem-seat, supersonic jet trainer, formed the basis for the F-15C air superiority fighter. The F-15C is currently in use by 5 countries around the globe, including Japan, South Korea and Israel. The F-15 features a superplastically-formed titanium, aluminium alloy, and carbon-reinforced epoxy airframe with a single bubble canopy cockpit. Compared to the analog cockpit of the Phantom II, the Eagle’s cockpit provides a wider field-of-view and thus improved situational awareness for the pilot. Another significant improvement over the F-4E which the F-15C had was the programmable AN/APG-63 radar with “look down, shoot down” ability, enabling the radar to distinguish aircraft and ground vehicles below the horizon. The AN/APG-63 was also able to identify targets through dense cloud, heavy rain, thick smoke, and snow, making it impervious to weather conditions. The F-15 was considered hefty when compared to the single-engine F-16. That said, the Eagle possessed a higher thrust-to-weight ratio, payload capacity and was much more aerodynamically stable than the F-16. Despite its considerable size, the F-15 proved that it was perfectly capable of holding its own in a dogfight, managing to outmaneuver a Northrop F-5 Tiger II fighter at subsonic speeds. Like the F-16, the Eagle is capable of pulling an impressive 9Gs in sustained turns, at the risk of the pilot blacking out and losing control of the aircraft. The F-15 maintains a perfect record of over 104 kills with zero losses in air-to-air combat to date.
