Rear Gun Turrets

The Halifax with the switch to Boulton Paul Turrets from the Frazer Nash (Parnall) of the Wellington (Wimpey). The Powered Turrets all had Reflector Sights. The F-N5 was a Gun Turret designed to replace the original Barnes Wallis Turrets used at the Front & Rear of the Wellington Mk I Bomber. The same Turret was later used as the Nose Turret of the Manchester, Stirling & Lancaster bombers, making it the most numerous British Gun Turret of WW2. In all over 22,000 F-N5 Turrets were produced. The F-N5 was developed under conditions of great urgency in the build-up to the WW2 between 1938 & 1939.

Halifax KN-W fellow Rear Gunner – smiling Flt Officer ‘Jock’ Jacks – RAF Elvington Station Gunnery Instructor

Boulton Paul was one of the 2 Main Innovators of Gun Turret Designs for British Aircraft, along with Nash & Thomson; they supplied large numbers of installations for British Aircraft. Boulton Paul’s designs were largely based on originals licensed from the French Company SAMM (Societe d’Application des Machines Motrices), while Nash & Thomson concentrated on the F-N Designs originated by the firm’s co-founder, Archibald Frazer-Nash. Boulton Paul’s Turrets were Electro-hydraulic in Operation; electric motors located in the Turret drove hydraulic pumps that powered hydraulic motors & rams. This was more effective than electric motors alone and did not require power developed by the Aircraft’s Engines as did the Hydraulic System utilised by the Nash & Thomson Design.

It was only Handley Page who opted for the BP designed Turrets and these were produced for fitting on the HP 57 (Halifax B1). July 7th, 1940 saw the 2 prototype Halifaxes, L7244 & L7245 tested with mock-up Turrets in position at Farnborough. L9485 was Air Tested with the 1st Type C & E prototypes Turrets fitted. During Air tests, there was severe vibration in the Front-Airframe of the Halifax. This turned out to be caused by turbulence made by the Nose Turret, which, when turned to either Port or Starboard made controlling the Aircraft difficult. What made things worse was that during Flight, air drag prevented the Turret from being centralised. Various modifications were carried out and although this improved things, there was still some ‘yawing‘ movement, which could not be entirely eliminated when the Turret was turned. The C Type MK.I was fitted after these initial ‘Teething’ Troubles were rectified.

Boulton Paul Type E Turret

The Boulton Paul Type E Turret was one of the most successful turrets produced and provided the Rear Defence for the Halifax. To the Front of the Gunner was the Control Table, through which the Operating Stick protruded. Above the Table was a Panel facing the Gunner with the main motor switch, sight switch & oxygen supply socket. Two Armrests were provided which were lowered into position when the Gunner was Seated, giving him some support and enabling him to control the Operating Handle accurately. Directly in Front was the Mk.III Reflector Sight fixed to an Arm which in turn was connected to the Gun Arms. Below the Gun was a 9mm Armoured Visor fixed on a Frame which moved in elevation with the Sight to provide frontal protection, although some Gunners had it removed to provide a better field of View. All-around visibility was adequate. but the rear downward View was somewhat restricted by the Guns & Controls. This was partly overcome by a feature which had been 1st used on other Turrets, which was when the Guns were depressed, 2 small Hydraulic Rams raised the Seat, keeping the Gunners line-of-sight parallel with the gun barrels and giving him a good View downwards. The 4 Browning Mk.II 0.303in Guns were mounted on their sides in pairs on either side of the Gunner, with the Cocking handles uppermost and within reach for stoppage clearance. Each Gun was provided with 2,500 rounds of ammunition, and the ammo boxes were fixed on the Port side of the Fuselage, well forward and remote from the Turret. Type E was a popular Turret with the Gunners, and over 8000 were produced. It was fitted to all Halifax Aircraft until the introduction of the Type D Turret armed with the larger calibre 0.5in Browning Guns.

Gun Turret Training Film 1

Gun Turret Training Film 2

The Nash & Thompson Type F-N.20 Tail Turret

This Turret was the most important of the Parnall Aircraft Ltd range, providing Rear Defence for most of the Aircraft of Bomber Command. The Designers at Oakcroft Road, Tolworth had been asked to re-design the F-N.4, incorporating modifications suggested by Gunnery Leaders on the Squadrons. An Armoured Shield was fitted, and the Gunner was provided with a Clear-vision Panel, but the main improvement was in the Ammunition Supply. The ammunition boxes in the F-N.4 were fitted in the Turret under the Guns, which limited the supply and affected the Trim of the Aircraft. A new supply system was devised in which large capacity boxes were fixed to the sides of the Rear Fuselage, the Ammunition Belts being taken from the Boxes along Steel Tracks to the Base of the Turret.

Entering at the Base by way of rotating right-angle elbow-joints, they were taken through ammunition booster units. These were needed because by the time the Belts had reached the Guns the weight was far too heavy to be pulled into the Breaches by the Gun feed mechanisms. The F-N servo feed units were an ingenious design in which powered sprockets were automatically energised when the belt pull was more than the Gun feeds could handle. The servo feed unit was driven by a hydraulic motor, 2 pipes connecting it to the pressure & exhaust lines of the Turret Feed System. The drive was transferred to the sprockets by 4 friction clutches. When the Guns commenced Firing, the Belts between the sprockets and the Guns tightened, and the platen arms moved across, engaging the clutches. If a belt jammed, an overload device disengaged its clutch. When the obstruction was cleared the clutch could be re-engaged by hand. Three 9mm (0.354in) Armour Plates, hinged horizontally and moving in unison with the Guns in Elevation, afforded protection to the Gunner’s Front. The Armour affected the Gunner’s field of View, and also limited the amount of ammunition that could be carried on some long-distance Sorties because of its weight. Some Groups decided that rather than set out on a long Trip with less than a full supply of Ammunition, a better weight-saving idea was to dispense with the Armour.

In common with most Turrets, when operating at the very low temperatures encountered on Night Operations, the Gunner’s View was often restricted by misting & frost glazing the Cupola. It was not uncommon for a Gunner to smash the Perspex Front Panel to give a better field of View. Although this added to his physical discomfort it was thought that the clear View was well worth a few degrees drop in temperature. The removal of the Front Panel soon became widespread, leading to an Official Modification to Turrets coming Off the line at Yate. The Front Panel was then mounted in slide grooves, allowing it to be dropped to give a clear View to the Front.

The gunner entered the F-N.20 from the Fuselage. After clipping his parachute to quick-release hooks just inside the Turret, he climbed into his seat and closed the Sliding Doors behind him, securing the locking catch. On early models of the Turret, during violent manoeuvres the catch sometimes gave way, allowing the doors to slide open. Without a Back-rest the Gunner fell back into the Fuselage and regained his position only with great difficulty. The catch was redesigned & strengthened. The Turret Controls were basically the same as in all F-N Parnall Tail Turrets, with some modifications.

The triggers on the twin-handled control column operated the 4 Palmer hydraulically Gun-firing valves via Bowden Cables. On some experimental F-N.20s used on High-Altitude operations, the triggers operated electrical switches controlling relays. The 4 Browning Guns were harmonised to a point 229M (250 yds) distant on to a 2.28M (7ft 6 in) square for Night Operations, and 366M (400yds) on a 1.52M (5ft) square for Daylight Sorties. The F-N.20 Turret was popular with Gunners, and, apart from the Clear-view panel and Door-catch, few modifications were needed.

All the usual ancillary services were fitted to the Turret. A provision was made for observing the angle of drift to assist the Navigator, and a more efficient form of oxygen supply was installed. This consisted of an oxygen economiser which regulated the supply to the Gunner according to demand. Problems had occurred with the old Type E oxygen masks, and a new mask, Type G, was issued at the time of the introduction of the F-N.20. This mask fitted the Type B Helmet, and few problems were encountered with the Oxygen Equipment after this.

The Gunner could Abandon the Aircraft by opening the doors, grabbing & clipping on his Parachute, traversing the Turret to the Beam-Stops, pulling the pin from his Seat Harness and falling out backwards. In the event of the Gunner being injured, another member of the Crew could release the door-catch from the Fuselage, and there was also a manually operated hydraulic valve outside the Turret which enabled the Turret to be turned from inside the Fuselage. This facility was added after Injured Gunners had been trapped inside with fatal consequences. If the hydraulic supply failed, the Gunner could turn the Turret by disengaging the rotation drive and turning a handle which operated a pinion acting on the gear teeth of the fixed Turret Ring.

When the 4 Brownings were Fired, cordite fumes would rapidly spread along the Fuselage to the other Aircrew positions, and prolonged Firing resulted in a heavy build-up of gases in the Turret. Ventilators were fitted in the top of the Perspex Cupola, but the problem was not fully overcome until an open direct Vision panel was fitted to aid Sighting. In the event of a Gunner being injured with the Turret turned to a Beam position, it was possible for another Crew member to turn the Turret from inside the Fuselage. A lever outside the Turret operated the rotation valve, and the doors could then be opened to assist the wounded Gunner. Seated in his position at the extreme end of the Fuselage, the Gunner felt completely isolated in mid-air: he could not see any other part of the Aircraft unless he traversed to one side, and several Gunners have mentioned the feeling of hurtling across the Sky completely alone. In early models, when the Turret was turned sideways the slipstream pressure on the Guns affected the Aircraft’s Trim. Pilots reported a marked effect on the Controls when the Gunner turned his Turret. The Trim was eased when 2 balancing Aerofoils were fitted: when the Turret was turned an aerofoil extended on the side opposite to the guns.

When the Wellington Mk.VI High-Altitude Bomber was being designed Parnall were asked to provide a Pressurised Tail Turret which was to be known as the Type F-N.70, but it was soon found that such a project would need new Technology, and the time needed was not available. The Wellington Mk.VI was eventually fitted with a remotely controlled F-N.20 Turret sighted from a Dome in the Pressure Cabin. In late 1944 a modified F-N.20 was introduced and, as this incorporated new parts, it was designated the Type F-N.120. The weight was reduced by 18Kg (40-lb) and some of the main structural members were redesigned. The most popular feature from the Gunner’s point of view was an improved Heating System.

Details of the Type F-N.20 Tail Turret

Position in Aircraft: Tail

Motive power: Hydraulic motor

Armament: 4 x 7.7 mm (0.3030 in) Browning Mk.II Guns

Ammunition: 2,500 rounds per Gun; 1,900 in Fuselage Boxes, 600 in Feed Tracks

Ammunition Feed: F-N hydraulic servo feed from Fuselage boxes

Gunsight: Mk.III free mounted Reflector Sight; Mk.IIC Gyro Gunsight

Fire Control: Palmer electric

Field of view:

Traverse: 94° to each Beam

Elevation: 60°

Depression: 45°

Weight of Turret (empty): 148 kg (325 lb)

Weight (Operational): 614 kg (1,350 lb) = Gunner – 82Kg (180-lb); Guns – 40Kg (88-lb); Ammo – 218Kg (480-lb); boxes – 15Kg (33-lb); Tracking – 23Kg (50-lb)

Diameter of Ring: (30½in)

Armour (when fitted): 9 mm (0.354in) armoured plates to Front aspect

Bomber Command Tracer Ranging

Though Tracer was known to be a misleading aid, on 8 April 1940 the Farnborough Gunnery Research Department issued a report to Bomber Command Gunnery Leaders entitled “The use of Tracer Ammunition as an aid to air sighting“. The reason for this was an unforeseen problem encountered by Rear Gunners. It was found that, when a Fighter approached on a ‘curve of pursuit‘ (a turning Attack, keeping his Guns aligned on the Bomber), it was very difficult to make a correct allowance for Deflection. This was because a Tail Gunner had nothing to tell him whether an attacking Fighter was moving across his line of fire or not. The Gunner had the impression of being suspended in space. After many novel ideas had been tried, it was found that the solution was the use of Tracer. The Tracer then in use was the Type G Mk IV, which burned to 549M (600yds). The theory was that this would help solve problems with both range & deflection. The advice given was:

As the Fighter approaches at long range fire a burst, keeping the centre dot aligned on the Target. You will see the Tracer rise to the centre of the ring, remain in a cluster, then move sideways in the Direction from where the Fighter has come. This gives a clear indication of the allowance required. Adjust your line of fire in the opposite Direction of the movement. Commence firing when the Target is just over ½-way along the trace, then maintain your Aim and keep firing until the Range closes to 138M (150yds) then fire Point Blank.

The amount of deflection was set out in a directive entitled ‘Zone system of sighting allowance’. It gave a series of allowances, such as: ‘when a fighter is seen in the sector between 10° and 30° deg round dead astern, allow 2 rads (radii of the graticule circle). This may seem complicated, but failure to grasp such advice could mean the loss of an aircraft and crew. Any fighter pilot engaging an aircraft with a skilful rear gunner did so at his peril. A Sunderland on convoy patrol off Norway was attacked by a group of Ju 88s which dived on the flying-boat in pairs. After an hour or 2 of the Junkers had been shot down, and the Sunderland returned to its base at Invergordon.

Various types of Tracer were designed by ICI Kynoch. One type burned red to 366M (400 yds), then a brilliant red, before ending in a puff of smoke. This was to warn the pilot that is ammunition was nearly spent. The G Mk III did not trace until 183M (200 yds), to avoid giving away the position of the Aircraft. The Luftwaffe did not use ball ammunition in its 7.92mm guns: ammunition comprised Tracer, AP and incendiary rounds.

No one epitomises the courage and heroism of the Bomber Command Veterans more than Freddie ‘Johnny’ Johnson from Tadcaster. A survivor of 92 missions during 5 years of service in WW2, the highly decorated Rear gunner was shot down twice – once behind enemy lines – but lived to fight another day