John Harrison's course notes from his gunnery course



John Harrison's course notes from his gunnery course


Hard back notebook with hand written and drawn notes and diagrams compiled when he was at No 2 A.G.S. at R.A.F. Dalcross in 1943. Twenty nine pages containing the theory behind gunnery, ammunition and the turret.


Temporal Coverage




Hard back notebook, twenty nine pages of handwritten notes and diagrams


This content is available under a CC BY-NC 4.0 International license (Creative Commons Attribution-NonCommercial 4.0). It has been published ‘as is’ and may contain inaccuracies or culturally inappropriate references that do not necessarily reflect the official policy or position of the University of Lincoln or the International Bomber Command Centre. For more information, visit and





[Front cover of book]

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7/4 [indecipherable word or character]

1590954 Harrison J.C.



B.P. TURRETS No longer on syllabus. 61 - 90
(Pages 70 -85 missing
F.N. TURRETS. 91 - 120
AMMUNITION 121 - 130
15 - 29.
40 - 59.

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[underlined] SIGHTS [/underlined]
[underlined] Mk. III Reflector Sight [/underlined]

Provides (1) Bead indicating where guns are pointing (2) a ring by means of which range is estimated (3) The radius of the ring subtends 10’ in every 100 yds., and is the correct deflection allowance for a crossing speed of 50 mph.

[underlined] Daily Inspection [/underlined]

[underlined] 1 [/underlined] Check for security of mounting.

[underlined] 2 [/underlined] Test bulb and 3 spares. Inspect for signs of [deleted] [underlined] 3 [/underlined] [deleted] blackness. If present exchange bulb, and in any case change after 50 hrs. or on each 40 hr. minor turret inspection.

[underlined] 3 [/underlined] Clean Sun Screen, Reflector Panel and lense. Anti Dim may be used to prevent condensation.

[underlined] 4 [/underlined] Check spare 5 amp. fuses.

[underlined] 5 [/underlined] Check electrical leads for faulty connections. When replacing bulb, black line on bulb should be to white line on holder. If put in wrong way round will result in fusing of the bulb on day switch and no light on night switch.

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[underlined] 30’ Class of Single Engined fighters [/underlined]

[table of ranges for guns]

[underlined] 50’ Class of Twin Engined Fighters [/underlined]

[table of ranges for guns]

[underlined] 60’ Class of Twin Engined Bombers [/underlined]

[table of ranges for guns]

[underlined] The Three Key Ranges [/underlined]

[underlined] 1 [/underlined] 600 yds. Limiting Range. Short Searing Bursts.

400 yds. Effective Range. Reasonable amount of ammo, may be used.

150 yds. Point blank range

Range estimation is essential when using tracer as an aid to sighting.

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[underlined] Bullet Pattern [/underlined]

[diagram of bullet patterns for a four gun turret]

Guns pointing at corner of a 7’-6” square at range of 400 yds.

[diagram of a bullet pattern for a two gun turret]

[underlined] Cone of Fire [/underlined] Spread of Bullets caused by vibration on gun. Cone of fire at 400 yds., 15ft. More than one Cone of Fire is called [underlined] Bullet Pattern. [/underlined]

[underlined] Gravity Pull on Bullets [/underlined]

At a height of 10,000’, Range 400 yds., a bullet will fall 5 ft. At a range of 600 yds. the bullet will fall 13 ft. For other ranges the bullet will

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[underlined] 4 [/underlined]

fall as follows:-

[table showing amount of fall of a bullet for a given range]

[underlined] Object of Harmonization [/underlined]

[underlined] 1 [/underlined] To aline [sic] the guns so that they form the appropriate bullet pattern.

[underlined] 2 [/underlined] To position the sight in the centre of the 4 guns.

[underlined] 3 [/underlined] To bring the sight down 5 ft. below the guns at 400 yds to allow for gravity drop.

[underlined] Use of short range Harmonization Boards [/underlined]

These boards are used as a matter of convenience for a range of 25 yds. The gunner must be careful to see that he uses the correct board for turret in use.

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[underlined] 5 [/underlined]

[underlined] BULLET TRAIL [/underlined]

Bullet trail is the distance the bullet lags behind the axis of the gun barrel due to air resistance set up by the forward speed of the gunners aircraft. The bullet always trails towards the tail of the gunners aircraft. This is allowed for by moving the guns towards the nose of the aircraft.

[underlined] Factors affecting Bullet Trail [/underlined]

[underlined] 1 [/underlined] [underlined] Range [/underlined] Increased - Bullet Trail Increased

[underlined] 2 [/underlined] [underlined] Angle of Gun. [/underlined] Maximum Bullet Trail on Beam. Minimum Bullet Trail Ahead or Astern.

[underlined] 3 [/underlined] [underlined] Speed [/underlined] Increased - Bullet Trail Increased.

[underlined] 4 [/underlined] [underlined] Height [/underlined] Increased - Bullet Trail Decreased.

[deleted] [underlined] 5 [/underlined] [/deleted] Code Word to remember these factors by RASH.

[underlined] Bullet Trail Lag [/underlined]

[table of bullet lag by range]

Make these allowances when the gun is at any angle within 450 of the beam. At any other angle ignore.

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[underlined] ZONE METHOD [/underlined]

Only applicable when dealing with an attack by a fixed gun fighter flying along a curve of pursuit.

[underlined] Curve of Pursuit. [/underlined] The path [deleted] of [/deleted] a fixed gun fighter [double underlined] must [/double underlined] take to keep take to keep its guns bearing. (To hold its deflection).

[diagram showing curve of pursuit]

Whenever a fighter is flying along a Curve of Pursuit, irrespective of where it is coming from, its direction of movement will always be towards the prolongation of the gunners axis.

[underlined] EVASIVE ACTION. [/underlined]

Evasive action of a Bomber is to turn into the attack, thus increasing deflection and forcing attacking aircraft to fly on a

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much tighter curve. A Diving Turn is usually adopted followed by Corkscrew evasive action. Evasive action is generally taken as soon as fighter makes his second dip of wings to start his Curve of Pursuit.

[underlined] [one deleted word] ONE METHOD FOR DEALING WITH FIXED GUN FIGHTER ON CURVE OF PURSUIT [/underlined]

[table showing deflection allowance]

The Zone Method is used for burst, after that check with tracer.

[underlined] TRACER [/underlined]

[underlined] Types in Use [/underlined]

G. IV — G. V — G. VI All burn from gun to 600 yds.

[underlined] G. IV. [/underlined] Bright daytime tracer. Colour Red.

[underlined] G. V. [/underlined] Dull night trace. Colour Yellow.

[underlined] G. VI. [/underlined] Bright daytime trace. Colour Red. Same

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as G IV, but a more perfect bullet.

[underlined] Point Blank Pattern [/underlined] (Check Harmonization).

[diagram of point blank angle]

Produced when firing a stationary gun on the ground or dead ahead or astern from an aircraft. Pattern produced by gun movement will show correct amount of deflection and bullet trail at 600 yds (ie the end point of tracer). It also shows the direction [deleted] the [/deleted] in which deflection must be made.

[three diagrams showing bullet angle]

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[underlined] The most important rules to use Tracer Correctly [/underlined]

[underlined] 1 [/underlined] Accurate Range Estimation

[underlined] 2 [/underlined] Maintain a constant deflection when firing sighter burst

[underlined] 3 [/underlined] Watch End Point of Tracer.

[underlined] Accurate Placing of Target on Trace [/underlined]

Can only be done when target holds off at a constant range. The gunner then has plenty of time to place the target on that part of the trace which corresponds to the range, i.e. 600 yds end of trace, 400 yds 2/3 along trace, and 200 yds 1/3 along trace.

On a Curve of Pursuit the range and deflection allowance is decreasing rapidly, and there is insufficient time for correct placing of target on trace therefore after firing sighter burst, place and keep target halfway along trace until range drops to 150 yds then fire point blank.

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[underlined] TACTICS [/underlined]

[plan view diagram of aircraft and turrets showing angles of fire]

[side view diagram of aircraft showing angles of fire from rear turret]

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[underlined] OPPORTUNITIES NOT TO BE MISSED [/underlined]

[underlined] Breakaway [/underlined]

Usually downwards to gain speed. Rear and Mid Upper Gunners advise other members of crew directions of breakaway, and at the same time firing continuously allowing one Radius deflection, until target has passed through the sight. Should the target be missed, the front gunner will give a 2 Radii deflection and [deleted] force [/deleted] fire on target.

[underlined] Downward Breakaway to Port. [/underlined]

[two diagrams of rear and front gunners view through sight]

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[underlined] Point Blank Pattern [/underlined] (Decisions when seen in sight)

[diagram of Point Blank Pattern.]

[underlined] 1 [/underlined] When firing dead astern or ahead

[underlined] 2 [/underlined] When firing on beam at a slower target when Bullet Trail and Deflection cancel each other out

[underlined] 3 [/underlined] When Target changes from approach to Curve of Pursuit.

[underlined] Combined Rules of Aiming [/underlined]

[underlined] 1 [/underlined] Identify aircraft.

[underlined] 2 [/underlined] Estimate Correct Range

[underlined] 3 [/underlined] Determine angle of attack and at 600 yds. fire sighter burst giving and maintaining the required zone allowance. Watch end of trace and re position target halfway along trace, and keep it there until range drops to 150 yds. Then fire point blank until breakaway.

[underlined] note. [/underlined] If paralell [sic] course target it should be positioned on trace according to range.

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[underlined] GENERAL NOTES [/underlined]

1. When on night operations always keep keen search on dark sky away from moon.

2 When on day operations always keep keen search on sky area around sun.

3. Search should be carried out so that M.U.G. is searching port side while R.G. is searching starboard. The rear gunner should search horizon down and Mid Upper horizon up.

4. It is advisable where possible for M.U. to give running commentary, as he has wider search view.

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[underlined] M.T.M. NOTES. [/underlined]

[underlined] BASIC [/underlined]

[underlined] HAMMERS [/underlined]

[underlined] Head [/underlined] High Carbon Steel, hardened on bases

[underlined] Shaft [/underlined] Straight grained ash. Classified by weight of head.

[underlined] DRAWING [/underlined [underlined] DESCRIPTION [/underlined]

[underlined] 1 [/underlined] BALL PANE for ordinary jobs riveting etc.

[underlined] 2 [/underlined] STRAIGHT PANE.

[underlined] 3 [/underlined] CROSS PANE

[underlined] 4 [/underlined] HIDE FACED where damage to job must be avoided as on all engine parts.

[underlined] FILES [/underlined] Material - High Carbon Steel.

[underlined] Cut [/underlined] Different arrangement of teeth are used for filing different materials.

[underlined] SINGLE CUT [/underlined] For soft materials. Teeth less likely to get clogged.

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[underlined] Double Cut [/underlined] For general engineering use most common cut.

[underlined] Dreadnought [/underlined] For heavy cutting.

[underlined] Rasp [/underlined] For very soft materials (wood, lead, etc)

[underlined] Rough [/underlined] For rough work only - to remove metal quickly.

[underlined] Bastard [/underlined] For ordinary engineering.

[underlined] Second Cut [/underlined] For good finish without too much time taken

[underlined] Smooth [/underlined] For good finish slower cutting

[underlined] Dead Smooth [/underlined]

For very fine finishing - use for final finishing only.

In describing a file state grade, Section, Length. eg. Bastard, Square, 8”, or Smooth Hard, Safe edge, 6”.

[underlined] Hints on Filing [/underlined]

[underlined] 1 [/underlined] Never use a file without a handle.

[underlined] 2 [/underlined] Remember files cut a forward stroke.

[underlined] 3 [/underlined] Keep files clean of chips by use of file card.

[underlined] 4 [/underlined] Use chalk for final finish, it prevents

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[underlined] 5 [/underlined] New files should be used on brass and similar metals. [deleted] New [/deleted] used ones on steel.

[underlined] CHISELS [/underlined]

[underlined] FLAT [/underlined] for general chiseling

[underlined] CROSS CUT [/underlined] for narrow grooves.

[underlined] DIAMOND POINT [/underlined] for cutting in corners and rectifying incorrect start when drilling.

[underlined] ROUND NOSE [/underlined] for cutting oil grooves and and rectifying incorrect start when drilling Chisels are forged from high carbon steel bars [deleted word] with cutting edge hardened and tempered. The rest is left soft and tough. The edge is ground to correct cutting angle for material to be cut. 75% for hard steel, 60% for ordinary steel, 40% soft materials.

[underlined] PUNCHES [/underlined] made from high carbon steel. Hardened and tempered at the business end.

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[underlined] CENTRE PUNCH [/underlined]

Right type.

Straight type for heavy work.

[underlined] PARRALLEL [sic] PIN PUNCH [/underlined]

Used to drive out Shackle pins, tight bolts etc.

[underlined] HOLLOW PUNCH [/underlined]

Used to punch definite sized holes in soft materials (leather, etc) Punch on end grain of wood to avoid damage.

[underlined] HACKSAWS [/underlined]

[underlined] COURSE TEETH [/underlined] Wide job cuts well correct

[underlined] FINE TEETH [/underlined] Wide job teeth clog incorrect

[underlined] COURSE TEETH [/underlined] [deleted] whole [/deleted] light job teeth straddle work in brake

[underlined] FINE TEETH [/underlined] light job several teeth in action cuts well correct.

[underlined] FRAME [/underlined] (Fixed or adjustable) Mild steel with wooden handle or composition

[underlined] BLADES [/underlined] High carbon or alloy steel, hardened and tempered.

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[underlined] FINE TEETH [/underlined] 22 - 32 teeth per inch - for thin metal

[underlined] COURSE TEETH [/underlined] 14 - 18 teeth per inch for thick metal

[underlined] DRILLS [/underlined]

[underlined] Material. [/underlined] High carbon steel or alloy steels. High speed steel drills can cut quicker than plain carbon steel drills - say twice as fast.

[underlined] Flat drills [/underlined] Simple to make drills inaccurate holes, slow cutting. wasteful of power.

[underlined] 1 [/underlined] [underlined] FLAT DRILL. [/underlined] [underlined] 2 [/underlined] [underlined] BOTTOMING DRILL. [/underlined] to finish bottom of blind hole.

[underlined] 3 [/underlined] [underlined] PEG DRILL. [/underlined] To machine surface around a drilled hole. To provide a good seat for a nut or a bolt.

[underlined] 4 [/underlined] [underlined] TWIST DRILL [/underlined] Designed as an efficient cutting tool. Must be correctly ground to operate well

[underlined] GRINDING [/underlined] Cutting edges must be of equal length and equal angle (590) to ensure

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that each does its fair share of work.

[underlined] REAMERS [/underlined]

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[underlined] BROWNING .303 MACHINE GUN. [/underlined]

[underlined] Mechanism [/underlined]

[underlined] Backward Movement [/underlined]

When round is fired recoil action takes place, continued expansion of gases drives recoiling portions to the rear. The Breech Block being locked to the Barrel Extension by means of the locking piece cam. Further rear movement of the barrel causes the locking piece pin to strike the slanting surface of the lock frame prongs, thus forcing the locking piece down the locking piece cam. The Breech Block then being unlocked is allowed to go further to the rear.

During the recoil action the barrel extension bears against the front of the accelerator causing the accelerator to rotate backwards as far as the stop. During this movement the ramps of the accelerator engage infront [sic] of the T shaped projection thus holding the barrel and extension to the rear. As the accelerator rotates backward the horns bear against the bent of the Breech Block, thus driving the breech block to the rear and compressing the return spring.

[underlined] Backward Action of Transporter [/underlined]

The claw of the transporter is engaged [underlined] infront [/underlined] [sic]

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of the rim of the Cartridge, lying against the Cartridge and Bullet Stops, and as the Breech Block goes to the rear this round is withdrawn from the belt and carried back being supported by the ejector. The transporter plunger rides along top of the front cam onto the rear cam and on reaching the champhered [sic] surface the plunger is depressed. The transporter ramp on the cover thus forces the transporter down and live round is placed on the face of the Breech Block.

[underlined] Extraction and Ejection [/underlined]

The empty case in the chamber is held by the Cartridge Rim Guides and as the Breech Block goes to the rear, [deleted] the round is withdrawn from the belt and carried back [/deleted] the case is withdrawn from the chamber, and being unsupported, it is free to fall off when clear of the barrel, if it does not then the downward movement of the transporter with the live round bears on it and forces it off. [deleted] whe clear [/deleted] In the case of the last round this is forced off by the ejector.

[underlined] Cocking Action [/underlined]

As the Breech Block moves to the rear, the Cocking lever is rotated on its axis and the nose withdraws the firing pin from the firing pin

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hole thus compressing the firing pin spring. The Point of the firing pin bears against the Sear compressing the Sear spring. The Sear under the influence of its spring returns ready to engage the bent when the cocking lever rotates on the forward movement.

[underlined] First Action of Belt Feed [/underlined]

The Stud of the Feed Lever is in the cam grove on top of the breech block, and as the Beech Block travels backwards the Feed Lever is rotated on its axis. The nose of the Feed Lever being engaged in the feed slide across the belt. The feed pawl rides over the round held by the returning pawl, and engages it ready for feeding. (The Belt during this action is prevented from leaving the gun by the retaining pawl and spring.

[underlined] FORWARD MOVEMENT [/underlined]

[underlined] Action of Return Spring [/underlined]

After recoil expands itself, the Return Spring re aserts [sic] itself and drives the Breech Block forward.

[underlined] Second action of Belt Feed [/underlined]

As the Breech Block moves forward the stud of the feed lever rides in the Cam Grove, and

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rotates the lever thus causing the feed slide to feed in [deleted] the [/deleted] a round which is brought against the cartridge and bullet stops.

[underlined] Forward Action of the Transporter [/underlined]

As the Breech Block rides forward the transporter plunger rides down the sloping surface, the round is still supported by the ejector, and further forward movement carries it into the chamber.

[underlined] Raising of the Transporter [/underlined]

When the spring and [deleted] one character [/deleted] plunger reach the front cam, they ride up the sloping surface at the same time the ejector is able to leave the cartridge (side ejector clearance). The transporter when it reaches the top engages the next round and rests on the [deleted] car [/deleted] top clearances.

[underlined] Forward Rotation of the Accelerator. [/underlined]

The Accelerator is rotated forward when the horns are struck by the bent of the Breech Block. This causes the ramps to disengage from the “T” shaped projection of the barrel extension, and Barrel and Barrel Extension are free to be driven forward by the Barrel Return Spring.

[underlined] Return of the Cocking Lever [/underlined]

As the Breech Block moves forward the

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the lever engages in the lever bracket and is rotated. This rotation engages the bent of the rear and firing pin, and the pin is thus free to travel forward when [deleted] returned [/deleted] released. At the same time the Cocking Lever is reset for cocking.

[underlined] Locking of the Breech Block [/underlined]

The Locking Piece Pin rides up the Locking Piece Cam and engages in the Lock Piece Recess in the Breech Block, thus locking the Breech Block in the forward position.

[underlined] Firing of the Cartridge [/underlined]

When the Breech Block is locked the lower lug of the sear is in line with the sear end of the fire and safe slot, and unit plunger is thus able to strike the sear which disengages from the firing pin bent. The Firing Pin is then carried forward by its spring and strikes the cap of the cartridge.

[deleted] Opert [/deleted] [underlined] Operation of Rear Sear [/underlined]

On ceasing to operate the controls the Rear Sear Lever is released and allows the sear to rise. The rear of the Breech Block depresses the Rear Sear which is forced upwards again by its spring when clear of the bent. The Breech

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Block on being forced forward by the return spring is arrested by the Rear Sear engaging the bent. The shock of the engagement is absorbed by the Rear Sear [deleted] engaging the Bent [/deleted] Buffer Spring through the medium of the Rear Sear Cradle. Should the Breech Block strike the Rear Sear before it was fully risen, resulting in partial engagement of the bent, as the sear is carried forward in this position, the sear projection strikes an inclosed ramp and forces the bent into full engagement.

[underlined] Barrel Fouling. [/underlined]

[underlined] 1 [/underlined] Powder Fouling

[underlined] 2 [/underlined] Chemical Fouling

[underlined] 3 [/underlined] Metallic Fouling

[underlined] 1 [/underlined] [underlined] Powder Fouling [/underlined] In the bore caused by solid products combustion

[underlined] 2 [/underlined] [underlined] Chemical Fouling [/underlined] Caused by forcing of the products combustion into the pores of the barrel. Dark colouration on a polished surface.

[underlined] 3 [/underlined] [underlined] Metallic Fouling. [/underlined] Caused by deposit of cupro nickel envelope being left in the bore. Whitish streak on the lands or roughness in the groves.

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[underlined] Removal [/underlined]

[underlined] 1 [/underlined] [underlined] Powder Fouling [/underlined] Type A cleaning oil on a 4 x 1 1/2.

[underlined] 2 [/underlined] [underlined] Chemical Fouling [/underlined] Requires 30 to 40 strands of 26 S.W.G. hard brass wire, soaked well in Type A. Used on a clean rod, and the effected parts [underlined] only [/underlined] are [deleted] cleaned. [/deleted] rubbed. Dry Barrel.

3. [underlined] Metallic Fouling [/underlined] Carefully watch Barrel for Metallic Fouling because this is the cause of inaccuracy and if excessive may lead to a blocked or burst Barrel.

Dissolve 2 K.N.N.S. Tablets (crushed in 40 c.c.s. liquid ammonia Specific Gravity .950 (Mixture is enough for on barrel only). Plug one end and leave standing for 30 mins. If nickel present colour dark greenish blue. Continue treatment until clear. Clean bore with flannelette and cleaning oil.

[underlined] Gauges [/underlined]

[underlined] .303 [/underlined] To ascertain wether [sic] fouling is present should pass through freely.

[underlined] .307 [/underlined] To indicate wether [sic] bore ware [sic] should not pass right through. If it does barrel U/S.

[underlined] .308 [/underlined] To indicate cord ware. [sic] Insert muzzle end, and it should not enter passed line on gauge, 1/4” from working end.

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[underlined] No. 2 Plug Lead [/underlined] Indicates barrel breech end ware [sic]

[underlined] Gun Loading [/underlined]

[underlined] F.N. 4 [/underlined] Bullets point outwards in tanks.

[underlined] L.H. Gun [/underlined] Double link to tank. Single link to gun.

[underlined] R.H. Gun [/underlined] Single link to tank Double link to gun.

[underlined] Note [/underlined] Tanks to be left in place when loading.

[underlined] F.N. 5. F.N. 13 F.N. 50 [/underlined]

Bullets point inwards in tanks

[underlined] LH Gun. [/underlined] Single link to tank, double link to gun

[underlined] RH Gun [/underlined] Double link to tank, single link to gun

[underlined] Note [/underlined] Tanks to be removed for filling

[underlined] F.N. 64 [/underlined]

As for F.N. 5 but tanks are to be left in place.

[underlined] F.N. 20 [/underlined]

Bullets nose outwards in tanks.

[underlined] LH Gun [/underlined] Double link to tank Single link to Gun

[underlined] RH Gun [/underlined] Single link to tank Double link to Gun.

[underlined] Note [/underlined] Tanks to be removed for loading.

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[underlined] BOLTON [sic] PAUL TURRET [/underlined]

[underlined] LAYOUT [/underlined]

[Hand drawn circuit diagram]

[underlined] Electric Driven Generator [/underlined] Dynamo supplying electricity the accumulator a 1000 Watt motor.

[underlined] Accumulator [/underlined] A resvoir [sic] containing electrical supply for whole of aircraft.

[underlined] Electric Distributor [/underlined] Means of conveying electricity from a fixed part of the aircraft to a moving part.

[underlined] Electric Motor [/underlined] A 24 volt, 40 amp. Motor. Normal revs 3000 per minute. High speed revs 5400 per minute

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[underlined] Epicyclic Reduction Gear [/underlined] Cuts down the revs from the Electric Motor to the Hydraulic Generator at a ratio of 5 to 3.

[underlined] Hydraulic Generator [/underlined] Consists of two banks of cylinders five in each bank, which generates pressure oil to work the rotational circuit.

[underlined] Hydraulic Jack [/underlined] This is a balanced type of Jack, that in it contains an equal volume each side of the piston head.

[underlined] Hydraulic Motor [/underlined] Means of rotating the turret.

[underlined] FUSES [/underlined]

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[underlined] ARMING AND LOADING [/underlined]

[underlined] HYDRAULIC GENERATOR [/underlined]

Driven by the electric motor through the epicyclic

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reduction gear, its function is to circulate oil under pressure to provide the power for rotating the turret or elevating or depressing the guns. It consists of two separate pumps, one for the rotational circuit and one for the elevation and depression circuit. The control column is connected to the guide ring of each pump, and according to the displacement of [deleted] oil [/deleted] the control column, the guide rings are set off centre to the pump imparting a stroke to the pistons, causing a suction of oil on one side and an output of pressure on the other side, which is passed to the Hydraulic Jack or the Hydraulic Motor. Reverse action of the control column reverses the direction of the pressure oil and consequently the direction of movement. The control column is so connected to the guide rings, that movement to right or left controls the rotational circuit and movement fore or aft the elevation or depression circuit. With the control column central the guide rings are concentric. Therefore no delivery of oil takes place and the turret is stationary. Speed of operation is governed by movement of the control column which in turn controls the volumetric output of each pump. For [sic] relief valves are connected

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with the distributor, 2 at 1200 lbs. for rotation and 2 at 750 lbs. for Elevation and Depression of the guns. Four gravity loaded ball valves are also connected to the distributor, 2 for each circuit. The hydraulic generator has a filler cap through which the complete system is filled. In the bottom of the generator is formed a sump.

[underlined] HYDRAULIC MOTOR [/underlined]

Converts energy into mechanical power to rotate the turret. Consists of a bank of 6 or 7 cylinders containing spring loaded [deleted] valves [/deleted] roller bearing [deleted] valves [/deleted] pistons which rotate about a central distributor inside an eliptical [sic] cam. The distributor has two inlet ports each connected to outlet ports, at an angle of 180% to each other. Oil forced into the cylinder force the pistons outwards causing the rollers to move towards the larger radius of the cam, thereby rotating

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which is the central part. If the flow is reversed the direction of the motor is also reversed.

[underlined] PRESSURE REGULATOR BOX [/underlined]

[underlined] Function [/underlined] Firstly to maintain a pressure on both sides of the Hydraulic Jack, [underlined] when the system is in operation [/underlined]

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[underlined] FRAZER NASH TURRET. [/underlined]

[underlined] LAYOUT (BLOCK) [/underlined]

[hand drawn diagram of a hydraulic system]

[underlined] RECURERATOR [sic] [/underlined]

Consists of a metal cylinder divided into 2 compartments by a fixed seal. The top compartment is called a reservoir and has a filler hole and cap. The lower compartment is called The Chamber of Variable Volume. A piston goes thru’ top of the Recuperator and is known as the Indicating Spindle. The main exhaust pipe only enters the bottom of the Chamber of Variable Volume. Attached to the base is a Release Valve, principle and operation being the same as the Relief Valve. Naturally both pipes enter into the Release Valve. Secured round the barrel is a strap (metal) which

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secures the pump, a hole communicating from the cylinder to the chamber. Underneath the strap are fifteen weep holes and two to three port holes.

[underlined] Function of [deleted] Pressure Regulator Box [/deleted] Recuperator [/underlined]

[underlined] 1 [/underlined] The only means of Filling and Bleeding the System

[underlined] 2 [/underlined] Maintain a static pressure of approx 16 lbs. per sq. inch through out the whole system when at rest. (To keep the air out)

[underlined] 3 [/underlined] Maintain a pressure of 12 - 20 lbs. per sq inch on the suction side of the pump when the system is in operation. (To ensure a constant supply of oil and prevent starvation)

[underlined] 4 [/underlined] To allow for variation in the capacity of the Hyd Ram due to its unbalanced piston.

[underlined] 5 [/underlined] To allow for variations in the volume of liquid due to change in temperature.

[underlined] E.D.P. [/underlined]

Consists of two cog wheels, one fixed and one free, rotating in different directions thus forcing oil under pressure through the teeth.

[underlined] Rotating Service Joint [/underlined]

There are two kinds of Joints Semi rotating, always fitted to the top of the turret, and Fully Rotating, always fitted to the bottom of the turret.

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[underlined] VALVE BOX [/underlined]

[hand drawn diagram of a valve box]

[underlined] Functions. [/underlined] To control operation of turret and elevation and depression of guns.

[underlined] V.O.M. [/underlined]

[two hand drawn diagrams of hydraulic pumps]

V.O.M. is the means of rotating the turret in either direction

[underlined] VOKES FILTER [/underlined] Fitted on exhaust pipe and cleans oil before [deleted] working [/deleted] it enters working parts.

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1 Release Valve

2 Relief Valve

3. Shearing Spindle on E.D.P.

4. Vokes Filter

[underlined] FILLING AND BLEEDING - FILLING [/underlined]

[underlined] 1 [/underlined] Gun rams at half stroke

[underlined] 2 [/underlined] Loosen union nuts on E.D.P, Exhaust first and then Pressure.

[underlined] 3 [/underlined] Remove filler cap and gauge filter on Recuperator, and clean. Fill Reservoir operating hand pump at same time. Pump slowly.

[underlined] 4 [/underlined] When clear oil appears at exhaust union, tighten union. Continue pumping until clear oil appears at pressure union then tighten union, but before tightening pump Recuperator Spindle up to 2”.

[underlined] 5 [/underlined] Continue pumping until spindle is fully extended. When it is fully extended pump for a further brief period to expel any air under the plunger.

6. Operate controls in all directions so as to fill up Valve Box and Slave Unions.

[underlined] BLEEDING [/underlined]

[underlined] 1st. [/underlined] Static [underlined] 2nd [/underlined] Pressure [underlined] 3rd [/underlined] Static.

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[underlined] 1st. Static [/underlined]

[underlined] 1 [/underlined] Unfasten bleed screw at top of ram body and operate controls for extension. Tighten screw when clear oil flows.

[underlined] 2 [/underlined] Unfasten screw on Ram Piston and operate controls for depression. Tighten screw when clear oil flows.

[underlined] 3 [/underlined] Check recuperator Spindle and pump until Spindle is extended to 4 1/2”.

[underlined] 2nd Power [/underlined]

[underlined] 1 [/underlined] Work turret for rotation and guns for elevation and depression, (Pumping as and when necessary) to displace air from units. Leave gun rams fully contracted and stop engine.

[underlined] 3rd Static [/underlined]

[underlined] 1 [/underlined] With Motor Valve released, operate triggers to discharge accumulator.

[underlined] 2 [/underlined] Disconnect rear sear hydraulic release

[underlined] 3 [/underlined] With trigger released slacken off bleed screws and bleed Palmer Firing Gear.

[underlined] 4 [/underlined] Pump until Recuperator Spindle is fully extended and continue pumping to expel all air.

[underlined] 5 [/underlined] With Gun Rams fully contracted bleed at all points until Spindle falls to 4”

6. Replace Filler Cap.

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[underlined] AMMUNITION [/underlined]

[underlined] BALL [/underlined]

[underlined] Base Markings [/underlined]

Makers Name
Roman Numerals
Purple Annulus

[two hand drawn diagrams of ammunition, base and side profile]

Ball ammunition can be recognised by [underlined] 1 [/underlined] Purple Annulus [underlined] 2 [/underlined] Roman Numerals VII on base of cartridge. [underlined] 3 [/underlined] Three indentations securing bullet to cartridge case

[underlined] ARMOUR PIERCING [/underlined]

[underlined] Base Markings [/underlined]

Makers Name
Mark W.1.
Green Annulus

[two hand drawn diagrams of ammunition, base and side profile]

Armour Piercing ammunition can be recognised by [underlined] 1 [/underlined] Green Annulus [underlined] 2 [/underlined] Letter W on base of cartridge [underlined] 3 [/underlined] Three centre punch marks securing bullet case.

[underlined] INCENDARY [sic] [/underlined]

[underlined] Base Markings [/underlined] Makers Name. Mark IV, V, VI, VII
Date Blue Annulus.

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[three hand drawn diagrams of side view of different marks of ammunition]

Incendary [sic] ammunition can be recognised by [underlined] 1 [/underlined] Blue Annulus [underlined] 2 [/underlined] Letter B followed by respective mark. Marks are B.IV (obsolete) BVI and BVII (Explosive Incendary [sic]

[underlined] TRACER [/underlined] Base Markings

Makers Name
Mark G. followed by respective mark.
Red Annulus.

[two hand drawn diagrams of ammunition, base and side profile]

Tracer can be recognised by [underlined] 1 [/underlined] Red Annulus [underlined] 2 [/underlined] Letter G. Followed by respective marks. [underlined] 3 [/underlined] Milled waist around base. [underlined] 4 [/underlined] Colour of tip of bullet is White for day and Grey for night trace.

[underlined] G.IV [/underlined] Is a [deleted] night [/deleted] day trace, has a white tip and burns from 0.600 yds

[underlined] GV [/underlined] Is a night trace, has a grey tip and

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burns dimly from 0.200 yds and then brightly from 2.600 yds

[underlined] GVI [/underlined] Is a day trace and has a white tip. It replaces GIV, the reason being that is a more perfect bullet.

[underlined] General Notes [/underlined]

If any bullet mark is followed by the letter Z it means that it is charged with Nitro - Cellulose instead of Cordite

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[underlined] PYROTECHNICS [/underlined]

[underlined] PYROS USED [/underlined]

[underlined] 1 [/underlined] [underlined] 1 1/2” Signal Cartridges [/underlined] fired from a number three Very Pistol. Colours Red, Green, Yellow, or Red & Green etc. Used for giving colours of day or as distress signals from Dinghy.

If the cartridge case has colours denoted by triangles, it means that one colour comes out first followed by other. If [deleted] coll [/deleted] colours are banded together it means they come out together and change colour in the air. First colour burns for 5 secs and second for 4 secs. Single colour cartridges last for approx 7 secs.

[underlined] 2 [/underlined] [underlined] Eliminating Cartridge [/underlined] fired from No. 3 Very Pistol last approx 9 secs and is used as a preliminary to 4.5”. Rear Flare.

[underlined] 3 [/underlined] 4.5” Rear Flare

[underlined] 4 [/underlined] 42 Fuse and 848 Fuse used for launching 4.5 Rear Flare

[underlined] 5 [/underlined] Aluminium [one indecipherable word] Marker

[underlined] 6 [/underlined] Flame Flare

[underlined] 7 [/underlined] Signal Marine Distress Mk III

[underlined] 8 [/underlined] 1 lb. signal Rocket.

[underlined] 9 [/underlined] Smoke Generator

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[underlined] PALMER HYDRAULIC FIRING GEAR [/underlined]

[hand drawn diagram of a hydraulic circuit]

When the turret Motor Valve is operated the Accumulator is charged. When the triggers are pressed the valve cuts off the exhaust pipe and connects pressure pipe to the guns. On [deleted[ ral [/deleted] releasing triggers the valve is returned by the spring. The pressure pipe is cut off and the guns are connected to the exhaust.

The accumulator ensures instantaneous firing, by keeping a reservoir of oil at a pressure of 240 lbs per sq inch.

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[table listing flights, dates, aircraft etc.]



John Harrison, “John Harrison's course notes from his gunnery course,” IBCC Digital Archive, accessed February 26, 2024,

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