Bombsight - Postwar Developments

Postwar Developments

The strategic bombing role was following an evolution over time to ever-higher, ever-faster, ever-longer-ranged missions with ever-more-powerful weapons. Although the tachometric bombsights provided most of the features needed for accurate bombing, they were complex, slow, and limited to straight-line and level attacks. In 1946 the US Army Air Force asked the Army Air Forces Scientific Advisory Group to study the problem of bombing from jet aircraft that would soon be entering service. They concluded that at speeds over 1,000 knots, optical systems would be useless - the visual range to the target would be less than the range of a bomb being dropped at high altitudes and speeds.

At the attack ranges being considered, thousands of miles, radio navigation systems would not be able to offer both the range and the accuracy needed. This demanded radar bombing systems, but existing examples did not offer anywhere near the required performance. At the stratospheric altitudes and long "sighting" ranges being considered, the radar antenna would need to be very large to offer the required resolution, yet this ran counter for the need to develop an antenna that was as small as possible in order to reduce drag. They also pointed out that many targets would not show up directly on the radar, so the bombsight would need the ability to drop at points relative to some landmark that did appear, the so-called "offset aiming points". Finally, the group noted that many of the functions in such a system would overlap formerly separate tools like the navigation systems. They proposed a single system that would offer mapping, navigation, autopilot and bomb aiming, thereby reducing complexity, and especially the needed space. Such a machine first emerged in the form of the AN/APQ-24, and later the "K-System", the AN/APA-59.

Through the 1950s and 1960s, radar bombing of this sort was common and the accuracy of the systems were limited to what was needed to support attacks by nuclear weapons - a circular error probable (CEP) of about 3,000 feet was considered adequate. As mission range extended to thousands of miles, bombers started incorporating inertial guidance and star trackers to allow accurate navigation when far from land. These systems quickly improved in accuracy, and eventually became accurate enough to handle the bomb dropping without the need for a separate bombsight. This was the case for the 1,500 foot accuracy demanded of the B-70 Valkyrie.