BRISTOL BLENHEIM, AIR MINISTRY BOMB SELECTOR CONTROL UNIT

Introduced in March 1937, the Bristol Blenheim was one of the first British aircraft with an all-metal stressed-skin construction, retractable landing gear, flaps, a powered gun turret and variable-pitch propellers. 

Although the Mk I was faster than most fighters of the late 1930s but the advances in the development of the new generation of modern monoplane fighters made all bombers more vulnerable particularly if flown in daylight.

For armament, the aircraft carried a single forward firing .303 Vickers VGO machine gun in the port wing while the rear gunner sat behind 2 x .303 Browning machine guns in the dorsal turret with another Browning fixed in a rear firing position under the nose blister. 

Like most contemporary aircraft, the Blenheim’s bomb bay doors were secured closed by bungee cords - relying on the weight of its 1000lb bomb load to force the doors apart when they were released. With no way of knowing how long it would take the bombs to force the doors open, bombing accuracy was extremely poor.

The Blenheim was fitted with the Mark III bomb sight which assisted the Navigator/Bomb Aimer in marking the target after he dialled in the Blenheim’s airspeed, altitude and angle of attack from his own set of repeater instruments located on a shelf above the navigation desk in the aircraft’s nose. 

Given the Blenheim was often needing to swerve and bank to avoid flak and enemy fighters during its bombing approach, bombing accuracy with the Mk III bomb sight was often haphazard and it was not until the introduction of ’stabilised & computer assisted’ bomb sights like the Mk XIV that RAF bombing accuracy really improved, although were never installed in the Blenheim.

Like most bombers, the Blenheim would could carry a wide range of ordinance from 14kg incendiary bomblets (carried in the Small Bomb Container SBC) together with 230 kg and 450kg general purpose High Explosive (GP/HE) bombs. 

Bombing missions varied greatly as did the targets which required the mission planners to not only choose the ordinance required, but also to determine the exact timing and sequence of the bombing runs. After the ordnance fitters had loaded the Blenheim in the dispersal area, the Pilot and the Navigator/Bomb Aimer were given a list of the bomb load configuration and the order they should be dropped. These were then inputed into the two Bomb Aimer Control Units:

• 16 x switch, Type F5D/655 Bomb Selector Control Unit
• 5D/1063 Bomb Preselector

The first of these Control Units - the 16 x switch, Type F5D/655 Bomb Selector Control Panel was mounted at knee height on the port wall of the pilot's cockpit just in front of the 5D/1063 Bomb Preselector Unit. 

The 16 switches of the F5D/655 related to 16 stowage points in the aircraft’s bomb bay and the crew used them to select which bombs or combination of bombs would be released over the target and which bombs might be retained for a later attack on a secondary target.

The knurled silver knob at the top right of the unit was rotated to activate pre-programmed settings which would appear in the small perspex window showing either: ‘Container Distributor’ - allowing for the release of the Small Bomb Containers or SBCs; ‘SAFE’ Except for Jettison’ - rendering the bomb load secure from release except for an emergency jettison; and ‘Singe & Salvo’ - enabling group release and ‘Stick’ bombing of targets.

Above this unit sat two small ‘Bomb Fuze’ units which could either arm the bomb load or render it safe

The second Unit  was the 5D/1063 Bomb Preselector which was programmed to ensure the bomb releases did not destabilise the aircraft’s flight characteristics during the attack. Carrying over 1000 kg of ordinance, without a balanced drop, the Blenheim could suddenly find its nose pitched violently upwards, hurtling it into the path of another aircraft in the bomber stream. Prior to mid 1940 the Blenheims had been using a more basic Rotary Bomb Preselector Unit as shown here:

Later and larger bombers such as the Vickers Wellington, Avro Lancaster, Halifax and Short Stirling carried a third Bomb Control Unit - the Type VII 5D/1065 Bomb Release Timer Distributor Unit which bomb aimers used to pre-set the timing interval and order of the ordinance to be dropped when attacking long, spread out targets such as a railway terminus, bridge or transport hub and needed to drop their bombs in a 'stick' formation along the target. 

This Air Ministry stamped 16 x switch, Type F5D/655 Bomb Selector Control Panel is an original WWII veteran Bomber Command Unit.
 
With its Air Ministry AM & Crown markings, this is a rare piece of RAF aviation history with all switches operational and the hinged, drop-down panel revealing the complex wiring for the unit. It also comes complete with its chain attached, removable Arming Safety Cover and original rotating 'Dial In' Arming Programs’

Mounted in its 100 yr old mango wood display stand with engraved plaque and highly detailed, custom built 1/72, or super detailed 1/48 scale model of this iconic aircraft perched above on its removable magnetic arm, this original Recovery Curios WWII aviation collectable also comes with a full colour, laminated Fact Sheet featuring photos of the instrument in situ with details on its operation and the aircraft’s history.
 

This Bristol Blenheim Collectable comes complete with detailed Scale Model, Mango Wood Stand & Plaque plus Printed Fact Sheet featuring photo of collectable in aircraft.

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