so it did not move relative to the ground even if the aircraft moved. Today these are known as an inertial platform. However, the large physical size of the CSBS series, especially the long drift bar, made it difficult to mount successfully on a platform. A compromise solution was designed as the Mk. XI, which mounted a single drift wire and iron sight on the front of a gyroscope taken from a Sperry artificial horizon that was already common in RAF use. This provided stabilization in the roll axis, which greatly eased the problem of sighting while maneuvering. In order to make it fit on the platform, all of the mechanical calculator portions of the sight were removed. Instead, the bomb aimer had to use manual slide rule calculators to find the drift and bombing angles, and then set the bombsight to these values. The bombsight was unable to quickly adapt to changes in direction or altitude, and in this case was even slower to calculate such changes. Very few of the Mk. XI designs were produced. Mk. XII and Mk. XIV, a new approach As if these problems were not enough, the RAF found in the training schools that it was all too common for the bomb aimers to dial in an incorrect setting, or forget to update one when conditions changed. It was planned that many of these problems would be solved on the Automatic Bomb Sight (ABS), which had been under development from before the war, and used very simple inputs from the bomb aimer to carry out all the needed calculations. Unfortunately, the ABS was even larger than the CSBS, and the demands for new bombsights to be stabilized would make it even larger and meant it would take some time before it could be brought into service. Something was needed in the meantime. The physicist and scientific advisor Patrick Blackett took up the challenge of fixing all of these problems at once, producing the Blackett sight with the Royal Aircraft Establishment. First, the manual calculator was replaced by an external box operated by a new crew member. The box contained the inputs needed to drive the vector calculator, as well as copies of the various aircraft instruments displaying the required information. The operator simply had to keep the input dials set so their indicators overlapped those on the instruments. Turning the dials drove the machine