Low Level Bombsight, Mark III
It featured a unique solution for timing the drop, projecting a moving display onto a reflector sight that matched the apparent motion of the target at the right instant.
It also saw some use in Bomber Command on the De Havilland Mosquito in the tactical role, and in a single case, on the Avro Lancaster.
This study also demonstrated that the aircraft were able to aim the bombs accurately in azimuth, but they had serious problems determining the proper instant to release them.
59 Squadron RAF reported that three aimers were selected to make bombing runs on a stationary target, and then again on one moving at 8 knots (15 km/h; 9.2 mph).
Bartlett and his navigator Pilot Officer Longmuir stated that the sight was a great advance over previous systems.
[2] Attacks over Biscay generally took place at night, and were carried out by eye with the aid of a Leigh Light.
[3] It was the problem of accurately determining range that had led both the RAF and Royal Navy to believe that torpedoes were "always considered to be the most effective weapon against shipping at sea.
"[4] This pre-war thinking proved to be largely wrong, and repeated attempts to attack convoys with torpedoes produced little result.
[5] A joint Admiralty/Air Ministry meeting on 11 June 1942 led to the formation of the Aircraft Torpedo Attack Committee to improve operations.
They demonstrated that torpedoes could only be dropped from low altitudes and speeds, or risked breaking upon impact with the water.
Henry Tizard sounded a contrary note in a January 1943 letter where he stated: Although I am one of those who have been enthusiastic about the Mark XIV sight and regret that it was not available for use long ago, I have a feeling that your ORS may be a bit too optimistic about its operational value against ships from a height of 4,000 feet.
By early 1943, a wholesale conversion to Strike Wings was underway, with slower aircraft like the Handley Page Hampden removed from service.
III through its development, and as its own operations expanded to include more tactical attacks at low level, Arthur Harris ordered it into production for Bomber Command use in October 1942.
The basic concept behind any bombsight is the determination of the range, the distance the bombs will move forward after they are dropped from the aircraft.
Acting alone, gravity will accelerate the bomb downward, and when this is added to the initial forward velocity given to it by the motion of the aircraft, the path becomes a parabola.
In addition, the wind can move the bomb as it falls, but given the well-streamlined shapes and high density, this tends to be relatively a small effect.
Looking along the line extending out the front of the bombsight, they would see if the bomber was going to pass over the target, and issue corrections to the pilot if it wasn't.
Measuring this wind is accomplished by looking through the bombsight at objects on the ground, and then calculating the angle needed to fly to offset this motion.
High-level bombsights generally spent a considerable amount of their design complexity on trying to account for the effect of wind.
[10] In the pre-war period, it was found that a significant source of error was due to the bombsight not being level with the ground when the bomb aimer was trying to sight through it.
This led to the introduction of simple stabilizer systems, today better known as inertial platforms, to keep the sights properly levelled in the roll axis as the bomber turned, eliminating these delays.
For this reason, a low-level bombsight simply doesn't need the same sort of windage correction complexity and can ignore it completely in most cases.
It is only when the aircraft begins to pass over the target that it has significant rearward motion, at which point it is too late to drop the bombs.
III was built in two separate components, the computor that calculated the range angle, and the sighting head that displayed this for the bomb aimer.
The separate computor cabinet was positioned on the left side of the fuselage, and two units were connected via an electrical cable.
XIV, which carried a standardized mounting system that clamped onto two vertical metal rods on the left side of the sight.
The mounting base also retained the system for turning the entire sighting head to the left or right, which the bomb aimer used to keep the vertical line centered on the target and to call any required corrections to the pilot if he noticed any sideways drift.
The altitude wheel was connected to the main part of the calculator, a large metal cylinder marked with lines showing the time it would take for the bombs to reach the surface.
The cylinder carried several sets of lines to account for the ballistics of different types of bombs and the number being dropped in a group, or stick.
As the aircraft approached the target, the vertical angle would increase and the bomb aimer would account for this by rotating the sight downward progressively.
