The Low Level Bombsight Mk. III consisted of two parts, the computor, and the sight(ing) head, shown here.
<p>The main part of the sight is a reflector sight, who's clipped-corner rectangular glass plate is roughly centered in the image. This displays a series of moving lines being projected from the large box on the left of the sight (to the back in this image). The bomb aimer dropped the bombs when the motion of the target was the same speed as the moving lines, a concept known as the "angular velocity method".
</p><p>In front of the main sight is a second glass plate that is used as a filter for night operations. It also has an associated metal shield, which is rotated to cover the plate in this case. Either or both of these would be rotated to the left of the sight during operation.
</p><p>The large cylinder at the bottom of the sight provides pitch stabilization. It was originally a Sperry artificial horizon that has been adapted so that its output tilts the entire sight fore and aft to account for any changes in the pitch of the aircraft. This was important in the low-level role, where the aircraft often approached the target from very low level and then began to pull up just before reaching it.
</p><p>The handle with the tag is used to rotate the sight up and down so it continues to over the target as the aircraft approaches. In its current position it has the sight pointed fairly down, which would be the case at the time of the drop. During the early approach the handle would be moved down, towards the stabilizer housing. This tilts the sight up, so the bomb aimer can use it while still far from the target.
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The handle projecting from the bottom (left bottom of the photo) is used to rotate the entire sight left or right to account for any crabbing or sideways drive.
Smithsonian Institution
<a rel="nofollow" class="external free" href="https://airandspace.si.edu/collection-objects/bombsight-sighting-head-low-level-mk-iii">https://airandspace.si.edu/collection-objects/bombsight-sighting-head-low-level-mk-iii</a>