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[Home] [Articles and Misc 103] [RAF Bombsights WW1 and WW2]

RAF Bombsights WW1 and WW2

103 Squadron 576 Squadron

For a bomber loaded with bombs and navigated to a distant target some kind of sighting device to enable the crew to drop their bombs accurately was required.

Known as a bombsight this device told the crew at which point their bombs should be released. Primitive bombsights were developed during WW1

As WW2 progressed the bombs became more advanced and so did the sighting problems. New bombsights were designed. During WW2 the RAF used two basic types of bombsight for its bomber aircraft, the vector sight and the tachometric sight.

The first had been in existence since 1918 with modifications and required the observer/bomb-aimer to compute and then feed in data before the attack for the aircraft's speed, altitude, the ballistic performance of the bomb and estimated wind speed and direction. On a small reflecting screen in front of him the bomb-aimer referred to a sighting cross made either from crossed wires or lines of light. As the aircraft made its bombing run, the right moment to release the bombs was when the centre of the sighting cross corresponded with the target beneath. The vector sight was simple and effective but only as accurate as the data fed into it and only if the aircraft made a straight and level approach to the target which was dangerous.

The tachometric sight computed wind velocity and direction automatically. A motorised sighting telescope was focused on a stabilised glass screen mounted beneath it. Linked to a gyro-stabilised platform the telescope enabled the bomb-aimer to view the target during the bombing run. Having programmed the sighting computer with the aircraft's altitude and the bomb's ballistic performance, the bomb-aimer adjusted a pair of knobs connected to an electric motor to maintain the telescope's sighting graticule over the target as viewed through the stabilised glass screen. Because the movement of the telescope relative to the platform was relayed to the sighting computer by the gyro stabilisation system, the computer generated a stream of signals which were relayed to the pilot (or directed into the autopilot if engaged). These were displayed on a directional indicator on his instrument panel for corrections to be made in the aircraft's heading, maintaining the sighting graticule accurately over the target. As the aircraft neared the target the angle of the telescope on the bombsight progressively reached a vertical position. Once it had reached the release angle calculated by the sighting computer, a pair of electrical contacts closed to form a circuit and the bombs were released automatically.

The following are the principal bomb-sights used by during WW1 and WW2 by the RFC and RAF, with the exception of the Dann sight which was a one-off design for use on the Ruhr dams raid.

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WW1 Drift Sight.

The original design was only suitable for low-level use and was later known as the Low Height Drift Sight Mk I. At higher altitudes the indicated airspeed, being measured by pitot tube instruments, was affected by differences in outside air pressure that rendered it increasingly inaccurate. The Mk. IA was introduced for this role, including a simple adjustment between the airspeed and altitude settings that accounted for this effect.

The Drift Sight was a significant improvement over earlier designs but it still required the aircraft to fly up or downwind on the final bomb run. For the RNAS this was a serious problem, as a submarine or ship would try to maneuver away which upset the bomb run. Over land as German anti-aircraft guns grew more accurate this became a serious concern as they would pre-sight for firing along the wind line and using the bombsight under fire was difficult. There were instructions how to use the Drift Sight for cross-wind bombing but these were complex and rarely used.

103 Squadron Drift Bombsight fitted to DH9

103 Squadron Drift Bombsight fitted to DH9

Drift Sight WW1

Drift Sight WW1

Drift Bombsight

Drift Bombsight

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Mk IX Course Setting Bombsight

From the outbreak of WW2 the Mk IX CSBS was in general use throughout Bomber Command. It was a pre-set vector sight used for night bombing of static targets when darkness prevented the target from being seen until the last minute. The sight was unsuitable for bombing while the aircraft was taking evasive action and its efficacy depended on the accuracy of wind computations. In January 1942 a modified version, the Mk IXA incorporating the Fourth Vector (moving target attachment), was designated for use in all Halifaxes and Stirlings. Bostons and Mosquitoes were fitted with the CSBS Mk IXE (minus the Fourth Vector attachment), and all other aircraft were equipped with CSBS Mk IXA (also minus the Fourth Vector attachment). Low-level attachments for the CSBS were issued to 2 Group in May 1942.

Course setting bombsight in Fairey Battle

Course setting bombsight in Fairey Battle

Course Setting Bombsight diagram

Course Setting Bombsight diagram

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Mk XIV Stabilised Vector Sight

Introduced in 1942 by 35 (Pathfinder) Sqn. The Mk XIV stabilised vector sight worked on similar principles to the CSBS but was more fully automatic, simpler to operate and better suited to use under war conditions. Evasive action could be taken up to the moment of bomb release and bombs could be released even with the aircraft making a banking turn to avoid flak or fighters, and even when climbing or gliding. In February 1943 use of the sighting head only was extended to aircraft of 2 Group in place of their CSBS Mk IXE. By mid 1944 most operational heavy bomber aircraft had been fitted with the Mk XIV sight. A modified version of the sight known as the Mk XIVA was trialled in July 1943 by 8 (PFF) Group. The Mk XIVA increased the operational height at which the sight could be used to 25,000ft and was first employed operationally in August 1944 by Mosquitoes of 8 (PFF) Group.

Mk XIV Stabilised Vector Bombsight

Mk XIV Stabilised Vector Bombsight

Mk XIV Stabilised Vector Bomb Sight and Computer

Mk XIV Stabilised Vector Bomb Sight and Computer

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T1A Bombsight

This American-built copy of the British Mk XIV sight differed little from the original except in minor details of construction and by the end of 1943 it was in use by all operational Wellington squadrons in the Command. By the spring of 1944 it started to replace the Mk XIV sighting head installations on OTU aircraft. The T1A bombsight was the American-built copy of the Mk XIVA and first saw operational use in July 1944 when Canadian-built Lancaster X aircraft arrived fitted with the sight. T1A sights were also fitted in the Mosquito in January 1945 in place of the Mk XIVA which were then in short supply.

….......

Mk II Stabilised Automatic Bombsight.

This precision tachometric bombsight was similar to the American Norden sight. The Mk II SABS had been fitted to aircraft of 97 and 207 Sqns by February 1943 and 61, 83 and 106 Sqns each had three aircraft equipped with the sight. Although it was more accurate than the Mk XIV stabilised vector sight it was withdrawn from use because the area bombing method used by the RAF on night raids did not require a precision sight and the need for a straight and level approach to the target was a disadvantage at the height of the area offensive. From August 1943 only 617 Sqn was equipped with a modified version, the Mk IIA SABS, for special precision bombing operations. By the end of WW2 617 could bomb a target from 20,000ft with an average error of 80yd.

….......

Mk III Low Level Angular Velocity Bombsight

Designed for use at up to 1,000ft and developed primarily for the bombing of submarines at low level, the Mk III low-level bombsight was also effective against land targets. It was introduced into service with 2 Group in May 1943 and also once used by 617 Sqn in 1944. Coastal Command had  priority on the issue of this sight. A few examples were acquired by 627 Sqn and 8 (PFF) Group.

….......

Dann Sight

This simple hand-held wooden bombsight was designed by W/C Dann at Boscombe Down for use by 617 Sqn on the Ruhr dams raid in May 1943. To achieve an accurate release point Dann used calculations based on the width between the towers of the Mohne dam to make a simple handheld triangular wooden sight. However this sight had its drawbacks. Buffeting of the aircraft at low level meant that it was near impossible for a bomb-aimer to hold the sight steady. Some dispensed with the Dann sight and experimented with their own sighting devices which included chinagraph pencil marks on the clear-vision panel and lengths of string attached to screws each side of the panel to create a large triangle. Laying prone some bomb-aimers thought this as a more stable position during the bombing run.

Compiled by David Fell. Photos from wiki and Smithsonian Inst

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