Key point: Washington wants a high-tech strategic bomber to penetrate enemy airspace. But part of that mission arguably should include the ability to shoot down enemy fighters.
Arming a bomber always came with trade-offs. For one, armament invariably increased the weight of the plane, necessarily reducing some combination of range, speed, and payload. Defensive weaponry also often had negative aerodynamic effects, leading losses in speed and maneuverability. Nevertheless, air forces began arming bombers from a very early period. The Gotha bombers that terrorized London during World War I experimented with a variety of different kinds of armament to defend themselves from British interceptors. A turning point in the search for the self-defending bomber came with the Martin B-10. The B-10 had three enclosed turrets for defensive machine guns, enabling it to defend itself on multiple vectors. Operating in concert, a formation of B-10s could theoretically protect itself from attacking fighters, and even incur serious attrition on a defensive force of pursuit aircraft.
The heyday of the self-defending bomber came during the interwar period, when theorists in the United States and (to a lesser extent) the United Kingdom hoped that well-armed bombers, flying in formation, could defeat attacking pursuit aircraft. The defensive argument performed two strategic roles, both increasing the chance that bombers would arrive over their targets to deliver payloads, and attriting away the defensive fighters of the enemy.
The USAF put the theory to test in the early daylight raids over Germany, and the results were far from good. The high speed and maneuverability of German fighters, combined with Germany’s “home field advantage” of anti-aircraft artillery, meant that formations could be broken up and individual bombers hunted down. Moreover, the machine guns carried by U.S. bombers were generally insufficient for warding off German fighters, which could punch at them with long-range 20mm cannon. The USAF eventually gave up on unescorted flights of bombers during daylight, instead turning first to night bombing, and then to long-range escort fighters such as the P-51 Mustang.
Bombers were nevertheless used in some other fighting roles, however. The Germans experimented with turning light bombers into night fighters, which could sacrifice maneuverability for speed, firepower, and sensors. Some Ju-88s and Do-217s were used in such a fashion. The Royal Air Force also used the de Haviland Mosquito light bomber as a night fighter in certain situations.
The immediate post-war bombers kept the dream of a defensive armament alive. The B-36 Peacemaker carried a 20mm cannon in a tail turret, as did the B-47 and the B-52. The USAF also famously experimented with turning the B-36 into a makeshift mothership with its own defensive fighter. However, most bomber designs of the jet age basically gave up on the idea of defensive armament. The B-58 Hustler carried no defensive weapons, nor did the XB-70 Valkyrie. As interceptors shifted from hunting with guns to hunting with missiles, a cannon offered little protection. Jet age bombers would depend on speed for protection, at least until it became apparent that they could not outrun SAMs. The last bomber designed to defend itself against enemy fighters was the B-52 Stratofortress, which carried 20mm Vulcan cannon in its tail. Although the accounts are disputed, B-52 tail gunners were credited with the kills of two Vietnamese People’s Army Air Force MiG-21s during Operation Linebacker II. Vietnamese sources attribute the loss of a third MiG to a B-52 gun in April 1972.
At one point, someone floated a half-serious proposal that involved equipping the B-1B with a mechanism for firing air-to-air missiles at pursuing targets, although it was unclear how the radar systems to guide such missiles were supposed to work. In a somewhat similar vein, thought has been given to modifying the B-1B to fit the missile truck concept, one version of an “arsenal plane” that would carry a large number of missiles but rely on sensors from other aircraft. The high speed and large payload of the B-1B would make it ideal for such a mission, at least among existing aircraft in the USAF inventory. Of course, the Air Force and associated analysts have also argued that drones could fulfill this role without the need for risking a manned aircraft.
The idea of a B-21 optimized for air-to-air combat makes some sense, given existing trends in the development of weapons and sensors. A large aircraft like the B-21 could carry numerous air-to-air missiles, even in stealth mode. Properly equipped, it could use powerful sensors to develop a good picture of the aerial battlefield, simultaneously acting as a fighting and command-control platform. Trends in bomber design have of late tended to eschew high speed in preference for stealth. Fighters, on the other hand, continue to prize speed in both offensive and defensive tactical situations. Firing missiles tends to reduce stealth, both because of the aspect change of the aircraft as it fires, and because of the evident existence of the air-to-air missiles. Fighters solve this problem by running away as fast as possible after shooting. The B-21 would likely require a different strategy, or very long-range missiles that would place it beyond the effective range of the enemy.
The idea of a bomber as fighter stems from several related problems. The USAF remains reluctant to completely entrust its deep penetration mission to the concept of stealth, both because of the evident practical difficulties (large bombers aren’t invisible during the day, no matter how stealthy they are) and because of concerns about improvements in sensor technology. Thus, the idea of a plane that could defend itself has some appeal. Moreover, as the cost of fighter aircraft has escalated dramatically, the idea of using a bomber to inflict serious damage on the defensive forces of an enemy has become more enticing. Finally, the general “capabilities creep” of proposed aircraft is almost necessary to building a strong, broad-based, and robust coalition for procurement. This can mean over-promising with respect to capabilities and missions. Whether the B-21 will ever actually try to shoot down an enemy fighter remains an open question; if so, it will become the first bomber since 1972 to successful turn the predator into the prey.
Robert Farley, a frequent contributor to The National Interest, is a Visiting Professor at the United States Army War College. The views expressed are those of the author and do not necessarily reflect the official policy or position of the Department of the Army, Department of Defense, or the U.S. Government. This first appeared earlier in 2019.