widely used, conversions and adaptations were quickly made to repeat the radar signal in the existing bombsights, allowing the bombsight calculator to solve the radar bombing problem. For instance, the AN/APA-47 was used to combine the output from the AN/APQ-7 with the Norden, allowing the bomb aimer to easily check both images to compare the aim point. Analysis of the results of bombing attacks carried out using radio navigation or radar techniques demonstrated accuracy was essentially equal for the two systems – night time attacks with Oboe were able to hit targets that the Norden could not during the day. With the exception of operational considerations – limited resolution of the radar and limited range of the navigation systems – the need for visual bombsights quickly disappeared. Designs of the late-war era, like the Boeing B-47 Stratojet and English Electric Canberra retained their optical systems, but these were often considered secondary to the radar and radio systems. In the case of the Canberra, the optical system only existed due to delays in the radar system becoming available. 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 , 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