Martin ball turret

Sperry Retractable Ball Turret
Sperry 250SH-1

The Sperry Lower Retractable Ball mounted in the belly of the PB4Y-1, is the deadly and efficient defender of the bomber's once soft underside. It was built especially for the PB4Y-1 whose ground clearance calls for a ball turret that can be kept out of the way on takeoffs and landings. Its guns sweep in a full circle and offer protection from any fighter who dips below the bomber's level. Its sight, the Sperry K-4, computes deflections automatically even when the gunner, swinging around below the plane, is unable to tell exactly which way he is facing.



turret assembly


An armor plate panel forms the bottom of the seat and extends up to the hinge of the door, protecting the gunner's trunk in battle position.

Facts and Figure
The retractable mechanism to pull the turret up into the belly of the bomber is simple. The big hydraulic cylinder is secured to a supporting beam in the top of the plane and the turret is suspended from a piston riding within the cylinder. A hand pump mounted on a fuselage wall supplies hydraulic pressure to force the piston up and raise the turret, which can be locked in place with safety hooks on the upper trunnion housing. A valve on the fuselage releases the hydraulic pressure and permits the piston and turret to slide down.

The Sperry Lower Ball operates hydraulically on pressure built up by a hydraulic pump driven by constant speed electric motor.

Its sight is the K-4 Sperry automatic computing sight, described in the Sights and Sighting section of this manual.

Azimuth limits

The turret can turn 360 degrees —a full circle—in azimuth.

elevation limits

In elevation, the turret guns can be lowered and raised from level (0 degrees) to straight down (—90 degrees).

PB$M silloute
The stowing position for the turret and guns after they have been retracted is 180 degrees azimuth and —22 degrees elevation.



Getting In

To start getting acquainted with the Sperry Ball, get in. You will have to be careful—men have been injured and even killed because they did not know the right way to get in, or were careless about it. The turret ball is heavy and yet delicately balanced; unless it is locked in place, it may swivel and break a man's leg or snap him almost in two as he attempts to enter. Remember also, as you step into the turret for the first time, that on combat missions you will never get in until your bomber is in full flight, and will always get out before the landing. The ball turret, hanging down beneath the plane, is no place to be when the bomber is moving along the ground. As you get in, take these steps carefully and in proper order. If you go about it right, getting into the turret is as safe as climbing into a rocking chair.

Be sure the elevation hand clutch is in the IN position. Remove the elevation hand crank from its clip on the outside of the turret. Slip it on the elevation hand control shaft.
Loosen the elevation hand brake—a small lever
beside the elevation hand control shaft.
Keep your left hand firmly on the hand crank.
Take the outside elevation power clutch handle from its clip, put it on the outside elevation power clutch shaft, and move it to the OUT position. This disengages the elevation power gearing, allowing free up and down movement of the turret. Unless you keep a tight hold on the hand crank, the weight of the guns will spin the turret down.
By turning the elevation hand crank with your
left hand, move the turret until the guns are pointing straight down at —90 degrees. This will bring the turret into position so that you can open the entrance door.
Keep your grip on the hand crank. Unfasten and
lift the door. Don't let the door fall back. To
prevent springing the hinge, never put excess weight on the door.

Activating the elevation hand crank



elevation cluch, hydraulic valve, hand pump

Still keep your grip on the hand crank. Reach down inside the turret, forward and behind the big elevation gear housing on the left, and move the inside elevation power clutch lever up to engage it. You will have to rock the elevation hand crank back and forth as you push the clutch in place. This re-engages the elevation power gearing, locking the turret firmly in gear.

Move the outside elevation hand clutch to OUT. Remove the hand crank and outside power clutch handle and replace in their clips.

Close the turret entrance door and prepare to lower the turret by closing the hydraulic valve.
Work the hand pump to lift the turret just enough to release the safety hooks.
Open the Safety hooks (A) to disengage them from the upper trunnion housing (B).
Open the hydraulic valve slowly, letting the turret ease down. Don't open the valve too fast.
Upper trunnion housing



Make sure that the turret is properly seated at its lowest position. Tapered bushings, mounted on the azimuth ring of the turret, should sit squarely in holes provided for them in the plane's floor ring. If they don't, jockey the turret until they do.

Make sure the master switch on the support beam is on.
Open the turret entrance door. Test the turret by grasping the supporting structure and putting your right foot on the seat. Try to work the turret with the pressure of your foot. There should be no movement. If there is movement, the elevation gearing is not engaged.
turret properly lowered
Gunner lowering himself into turret15
Lower yourself into the turret by grasping and swinging down on the support frame. Put your right heel on the right foot rest, then your left heel in the range pedal—being careful not to throw your whole weight on the range pedal.

Fasten the safety belt. Close and fasten the entrance door. Make sure that the door latches are securely closed. Then you are ready to go.
Closing entrance door




1 Make sure the azimuth power clutch is engaged—the lever at the upper right should be down.
Flip on the main power switch—a toggle switch under a wire guard on the junction box beside your left knee.
Right beside the power switch are the two gun selector switches for firing the guns separately or together. Flip both of them on.
Turn on the sight switch directly in front of your nose on the sight. Turn the sight rheostat beside it to adjust the brightness of the light. Never operate the turret under power with the sight switch off.
5 Finally, grasp the two handgrips. Don't worry about safety switches—the turret has none. But, notice that in azimuth the controls work exactly opposite to all other turrets. To move the turret right, swing the handgrips to the left; to turn left, swing them to the right. Pull back on them to tilt the turret and guns up, and press forward to turn the turret and guns down. Don't jerk. Steady, smooth tracking is especially important in using the Sperry sight.
The other controls you will use in combat are right at hand. On the top of each handgrip, under your thumbs, are firing buttons, used instead of triggers on the Sperry Ball. The fuses which protect the Sperry's electrical circuits are in the junction box beside your left knee, where you found the main power switch. For charging the guns, you will find two handles next to your feet. Reach down to the floor, arms crossed, and pull the handles up carefully until the slack is out of the cables. Then pull them up sharply all the way. Don't ride the cables on the return action; allow them to go back under their own power, still keeping your hands on the handles.

. . Where to Find the Controls
. . How to Use Them

Once you are seated, the controls and switches of the turret are spread before you. Check clutches and turn on the switches in exactly the order shown here.

main power and gun selector switches

sight switche

hand grips

Left hand pulling to left, right hand pullilng to right



Using Auxiliary Equipment

Auxilary Units identified

You will find a demand type regulator with a hose connection for your oxygen mask right under your seat. Alongside your right ear is the flow and pressure gage. The oxygen is drawn from the plane's central tanks in most models. The heated suit plug-in is also under your seat. The interphone jacks for your headphone and throat microphone lead out of the junction box. A trouble light is clamped in a clip just under top rim of the ball to the left of your head. By your right foot is a new azimuth turret position dial, in which a cutout of your guns rotates
upon a clock face and shows you your azimuth position at all times. For manual operation of the turret in emergencies, shafts designed for use with removable hand cranks are on the right and left side of the turret—right for azimuth, left for elevation. The hand cranks are stored in clips above your head.

To change to manual operation:
1 Turn off the main power switch.
2 Remove the hand cranks from their clips and place them on the shafts.
3 Disengage azimuth and elevation clutches.



Getting Out

1. To get out of the turret, drive it to—90 degrees in elevation, so that the guns point straight down; this will bring the doorway into place in the floor of the bomber. At the same time, drive the turret to 180 degrees in azimuth—six o'clock on your azimuth turret position dial.
Turn off all switches. Open the door and step out. Close the entrance door.
2. Close the hydraulic valve.
3. Using the hand pump raise the turret until the safety hooks can be closed.
4. Close the hooks. They must catch the flange on the upper trunnion housing to hold the turret securely.
5. Use the elevation hand crank to crank the guns to —22 degrees elevation. (The turret will already be at 180 degrees azimuth.) You will know that the guns are at —22 degrees when the elevation switch cam, a raised metal plate

The retracted turret

fastened to the upper curve on the ball, moves up as you turn the ball in elevation, and presses against the elevation retraction position switch, throwing it on. This switch flashes a light in the pilot's compartment to tell him when the ball turret is retracted and the plane is ready to land.
6. Engage the outside elevation power clutch, using the handle in the clip on the trunnion ring support. Replace the handle in the clip.
7. Tighten the elevation hand brake and replace the hand crank in its clip. Always make sure the clutch handle and crank are in their clips.


Don't worry about the possibility that the hydraulic retraction gear might get out of order in flight—if it does, you can still raise the turret by means of the plane's bomb hoists. These hoists are two winch, cable, and pulley units mounted on the top structure of the plane on either side of the turret position. Use them only in an emergency when the retracting mechanism won't work.

Emergency hand crank
Getting Out Operating hand crank



1. Run the guns to 180 degrees azimuth and —90 degrees elevation and get out of the turret.
2. Unwind the winch cables and feed them over their opposite pulleys—the rear winch cable over the front pulley, the front cable over the rear pulley. Hook the ends of the cables into the top of the turret hanger assembly.
3. With the assistance of one of your crew mates, crank both winches at the same time, evenly and slowly, until the turret is raised enough for the retraction safety hooks to catch and support the turret. Close the safety hooks. Then crank the guns up into their stowing position—about -22 degrees elevation—just as you do after normal retraction of the ball


Preparing the Turret for Combat
With the working information contained in the preceding pages—and sufficient practice tracking with the Sperry sight—you could easily take over the Sperry Ball in combat. If you specialize in this turret, however, that will be only part of your job.
The rest of your job—adjusting sight and guns and loading ammunition for a mission—is explained in the following pages.
The Sight
K-4 gunsight
The K-4 is an upside-down type of automatic computing sight built especially for the Sperry Ball. Held by a single long mounting pin, it hangs down from the sight cradle on a level with your head. Connected to the sight are three flexible shafts which bring it the turret movement and range data needed for computing deflections. The upper shaft entering the top rear of the sight revolves as the turret moves in azimuth. The lower shaft at the top rear revolves as the turret moves in elevation. The third shaft, on the left side, leads to the range pedal, which you move with your left foot to frame the target in the sight reticles.



Adjusting the Guns
The guns are mounted in the Sperry Ball to feed from the outside—the right gun feeds from the right and the left gun from the left. The guns are held in their cradles by a rear trunnion block and slide (A) and two front trunnion studs (B). The rear trunnion block, attached to the rear mounting holes of the gun, dovetails into the rear trunnion slide—merely check it to make sure that it rides snugly in the slide. The front trunnion studs, which screw into the front mounting yoke of the cradle and into threaded holes in both sides of the gun adapters, must be safely wired.
Interior of turretSpecial charging units (C) are installed on the inside plates of the guns, with mounting bolts which must be safety wired. The cable connection to each unit must have a cotter pin (D). Special link ejection chutes (E) are installed on the inside of the guns, where they are held by the guns' belt feed pawl pins and cotter pins. The guns can be adjusted up, down, or sideways in their cradles by using an adjustment screw and bolt assembly provided on each rear trunnion.


Adjustment screw and nuts

To make the adjustments:
Loosen the vertical lock nuts and adjustment nuts.
Loosen the lateral lock nuts. |
Turn the lateral adjustment screws on each side of the mount right or left to move the back of the gun from side to side.
Turn the vertical adjustment nuts right or left to raise or lower the back of the gun.
When the gun is in its proper position, tighten all lock nuts.
By means of these adjustments the guns can be centered in their mounts.
To center them you will have to move the adjustment screws and nuts back and forth until you find the approximate center of both the lateral and vertical adjustment movements. With practice, you will be able to center a gun quickly and with little error.



the Guns and Sight

There are a number of ways to harmonize the Sperry Ball's guns and sight. Because of the Ball's computing sight and compact construction, they are more complicated than the procedures for other turrets. In all cases the sight must be removed and reinstalled in the turret to do a good job. The handiest method for gunners is to boresight the guns and line up the sight on some small object, such as a tree or a chimney, at least 1,000 yards from your plane. This is known as the field, or distant object, method of harmonization.

First move the guns to zero elevation. Get out of the plane, remove both gun access plates from the ball, and the backplates and bolts from both guns. (Or you can use a boresight reflector to enable you to sight through the barrels without removing the parts.) Open the turret door.
Then center one gun in its mount, as directed on the preceding page—and you are ready.

Removing access plate

Disengage the azimuth and elevation power clutches. Line up the centered gun on the object selected, using the hand cranks to move the turret until the object is exactly in the center of the gun bore. Then lock the turret in this position by re-engaging the azimuth and elevation power clutches.
Line up the other gun on the same object by turning its vertical and lateral adjustment screws and nuts. Don't move the turret as you do this. When you have the object exactly in the center of the gun bore, tighten all lock nuts.

Disconnect the electric cable and all flexible shafts at the sight—except
the azimuth rate shaft, which can be disconnected more easily from the turret gearing, leaving it attached at the sight. Remove the lamp and slip out the deflection dial cover. Then set the target dimension dial on the sight at 20 feet and the range dial at 1,000 yards, using a flexible shaft to rotate the range dial.

Using flexible shaft to rotate range dial

Illustration of gun harmonizing



Setting deflection dials to zero
Turning thumb screws

Then set both deflection dials to zero, using a piece of flexible shaft, or the range shaft, in the elevation input, and the azimuth shaft already in the azimuth input, to rotate the dials.
Sighting through the optic head, use a screwdriver to turn the thumbscrews on the azimuth and elevation deflection dial shafts until the reticles are exactly centered on the same object the guns are boresighted on. If daylight shining through the lamp aperture is not sufficient to light up the optic head and reticles, use a flashlight or your trouble light.
Check the deflection dials to make sure they have not been moved off zero in this operation. If they have, return them to zero and then center the reticles on the object again. Replace the deflection dial cover.

handcranking to zero aximuth and zero elevationRemoving sight from mounting bracket
Move the turret by hand crank to zero azimuth and zero elevation and lock by reengaging the azimuth and elevation power clutches.
Remove the sight from its mounting bracket by unlocking and withdrawing the long mounting pin. Handle the sight carefully.



Flexible Shaft Connections
Set the azimuth and elevation position dials to zero, using the azimuth shaft to rotate the azimuth dial and a piece of flexible shaft to turn the elevation dial.
A Elevation gear unit
B Elevation rate input shaft
C Sight
D Range shaft to range pedal
E Electric cable
F Azimuth rate input
G Azimuth gear unit
Connect the electric cable and install the sight in the turret.
Connect the elevation shaft to the elevation input on the sight —and the azimuth shaft, which was left connected to the sight, to the turret. Make sure you do not move the azimuth and elevation dials off zero in doing this, and make certain all connections are secure.
Connect the range shaft to the sight's range input and disconnect it from the range pedal. Rotating the shaft with your fingers, turn the range dial as far past zero as it will go, then back it off a quarter turn of the flexible shaft. With the range pedal all the way up, connect the range shaft to the range pedal again
flexible shaft connections


Another method
Another method of harmonizing the Sperry Balls to line up the guns and sight on a special pattern stand, such as the one illustrated here. Set up the stand as level as possible at least 50 yards from the plane. Then boresight each gun on the pattern and line up the sight on the sight cross, using the same procedure as outlined above.

sight pattern



Loading Ammunition
Two ammunition cans, which are a permanent part of the turret ball, one for each gun, hold approximately 500 rounds of belted ammunition apiece. In some late modifications of the turret the ammunition cans are placed outside the turret, mounted to the hanger assembly, to give the gunner more room; flexible chutes carry the ammunition belts from the cans to the turret and guns. But most Sperry Ball turrets still have cans installed right in front of the gunner. They cannot be removed from the turret and must be loaded from the outside.

removing the cover plate

The method:
First remove the ammunition can cover—a plate in the turret surface held by four Dzus fasteners, or by two cover latch screws in later models.

Note that the cans are equipped with baffle plates to insure positive feeding and to keep the ammunition from tumbling about.baffle plates




Start with the single-link end of the belt first, so that the double-link end will feed up into the gun, and fold the belts into the cans in the pattern shown in the diagram. Force the belts down through the chutes to the guns. By putting pressure on the ammunition in the chute, the first round will move into the feedway, over the belt holding pawl. Caution: Fasten the ammunition can cover securely after loading.

Belt feeding patterns


Pre-Flight Routine . . . follow it step by step
(The plane should be over a testing pit to allow normal movement of guns.)
1. Install the guns' barrel and oil buffer groups —leaving out bolts and backplates.
2.. Check harmonization of sight and guns by boresighting on an object at least 1,000 yards from the plane, or a pattern stand.
3.. While harmonizing the guns, make sure the manual system is working properly.
4.. Make sure the gun bolts are assembled properly, to feed from the right in the right gun and from the left in the left gun. Then install bolts and backplates in both guns.
5. Try to rock the guns in their cradles to make sure their mounts are secure. Check to make sure the rear trunnion blocks fit securely in the rear trunnion slides, and that the front trunnion studs are safety wired.
6. Make sure the bolts mounting the charging units to the inside of the guns are safety wired and cable connections have cotter
7. Inspect the electric cables. Make sure all cannon plug connections are tight. Report any frayed or damaged cables.
8. Make a visual check of the fuses in the junction box, using your trouble light. If any are burned out, have them replaced. (The spare fuses carried in the spare parts box should be saved for combat emergency.)
9. At the same time, check your trouble light. Turn on the switch and make sure the bulb is bright.
10. Check oxygen and interphone connections in the turret.



11. Inspect all hydraulic lines. If you find excessive leakage, report it immediately.
12. Check the round gage on the side of the oil breather tank. If oil is not level with the bottom of the gage window, report it.
13. Make sure the plexiglas and safety windows are clean.
14. Enter the turret correctly— with care.
15. Make sure that the inside azimuth and elevation power clutches are engaged.
16. Turn on the main power switch.
17. Flip on the sight switch. The sight motor; should start, the sight bulb light up. Turn the sight rheostat to check operation. Make sure the optic head is clean.
18. Check all input shaft connections to the sight. Make sure they are tight.
19. Work the range pedal with your foot to make sure the reticle moves in response.
20. Make sure both gun chambers are empty. Then turn on both gun selector switches. Check the guns' headspace. Pull one trigger at a time, charging the guns each time, and check the Electric Triggers for proper adjustment—listen for a "click" as the firing pins of the guns release.
21. Turn off right gun selector switch, and make sure either trigger operates the left gun's Electric Trigger. Then turn on right gun selector switch and turn off left gun selector switch. Make sure that each trigger sets off the right gun's Electric Trigger.
22. Run the turret under power in azimuth and elevation, to check on ease of operation. Run the guns up to the fuselage to make sure the limit stops are working. Then stop the turret and check for creep.
23. Check the fire cutoff system by swinging the guns on the propeller and antenna loop areas of the plane and attempting to fire. Make sure the guns cease firing

with the proper amount of safety margin —your crew chief will tell you how much.
24. Put on your oxygen mask, connect it, and test by turning on the direct flow valve. Check gage for proper pressure, as determined by your crew chief. Close valve.
25. Plug in your headphones and microphone to test whether your crew mates can hear you and you can hear them.
26. Plug in and test your heated suit and operation of the rheostat.
27. Get out of the turret and inspect ammunition belts to make sure the rounds are in good condition and properly belted.
280. Load both ammunition cans and feed the double-link end of the belts down through the chutes into the feedways of the guns.
29. Make a last visual check of the turret.
30. From outside, move the turret to stowing position so that it is ready for the takeoff.

Before Landing
1. Clear the guns by opening the gun covers and then hand charging the guns twice.
2. Run the turret to 180 degrees azimuth and —90 degrees elevation. Turn off all switches, Then get out and retract the turret up to stowing position for landing.

1. Remove the ammunition can cover and clear all ammunition from cans and chutes.
2. Field strip the guns.
3. Clean the gun casing groups, inspecting their parts as outlined under the post-flight check in the Guns section of this manual.
4. Then detail strip the parts removed from the guns, cleaning and inspecting them as outlined in the Guns section.
5. Report any malfunctions of turret or guns noted on the mission.



Bendix upper deck turret

The Bendix Upper Deck
Bendix 250CE-3 & 4

The Bendix Upper Deck Turret is an all electric turret used exclusively in the PBJ Mitchell bomber where it protects the upper area of the plane. There are two basic models: the Bendix 250CE-3 and the Bendix 250CE-4. The Bendix 250CE-3, used only on early models of the PBJ, is mounted just back of midship. When waist guns were introduced to the PBJ, the Bendix 250CE-4 was designed for mounting just aft of the pilot's compartment. The two models are essentially alike. The description of the Bendix 250CE-4 in the following pages will also enable you to operate the Bendix 250CE-3.



Facts and Figures

Elevation limits


The Bendix Upper operates electrically on power supplied by the bomber's central system.

Its sight is the N-6A or N-8 optical, fully described in the Sights and Sighting section of this manual.


In elevation, the turret can be lowered and raised from horizontal (0 degrees) to almost straight up (82 degrees).

The turret has two speeds—normal tracking speed and high speed.

Armor plate on the turret housing protects the gunner in front, no matter where he aims his guns.

Azimuth limits

PB4Y-2 silouette upper deck turret locations

The turret can move 360 degrees—a full circle —in azimuth.

The stowing position is 0 degrees elevation and 180 degrees azimuth-guns level and pointing straight back toward the tail.



Getting In

To start getting acquainted with the Bendix Upper, step right in. You won't have any trouble —this is one of the easiest of all turrets to enter and operate.

Adjust the footrests to fit your own height by moving them up or down in the notches on the foot slide.

If you prefer—and a few trials will show you if this is the easiest method for you—you can snap the seat up to its locked position before you get in. Then stoop into the turret, throw one leg over the seat as if you were mounting a high bicycle, and pull yourself up by the inner turret supports.

Adjusting footrest and seat

Or you can leave the seat down, step up on the footrests, pull yourself up by grasping the inner turret supports, brace one elbow over one of the supports, and with your free hand pull up the seat to its locked position beneath you. When you are seated, your eye should be level with the sight. If not, adjust the height of the seat by turning the small handle and swivel on the right side of the seat support, loosening the band that holds the seat to the central column. Slide the seat up or down on the column until you have it just where you want it. Then reverse the handle, tightening the seat in place, and you are ready to go.

Steping up




. . . where to find the controls
. . . how to use them  

You can get the turret into action about as quickly as you could start an automobile on a warm summer day. First reach outside the turret to the left wall of the fuselage; there you will find a long, narrow box with two switches mounted on it. One is the main power switch; turn this one on first. Then flip on the heat-light switch right beside it, which shoots power to the sight bulb, trouble light, and heated suit unit.
Use the sight rheostat (D), on the controller housing just above the left handle, to adjust the brightness of your sight bulb to outdoor lighting conditions.
Then grasp the control handles so that the bottom edges of your hands press down the two safety switches (C). As long as either one of these switches is held down, the turret is ready to operate. With the switches up, the turret won't move.
Turn the handles just as you would steer a bicycle—to the right to go right, left to go left. Press down on the heels of the handles to raise the guns. Pull up on them to lower the guns. Move the controls smoothly and deliberately, and you will be able to track any target closely and with deadly aim.
The other controls you will need in combat are practically at your fingertips.
Right under your index fingers on both control handles are the triggers (B).
On top of each handle, by your thumbs, are the high speed buttons (A) that give you extra speed for changing quickly from one target to another.
In front of your hands at the back of the controller housing are two shiny metal disks that are your push-to-talk buttons (E). Pressure on either disk opens the interphone system for you to speak.



Chargeing unis on foot steps
The charging units are your footrests. To charge the guns, draw the foot rests up as far as they will go in their slides with the toe of your shoe, then step down on them sharply.
Using the Auxiliary Units

Because the Bendix is used only in the PBJ, a low-level bomber, it has no oxygen system. But it has all the other standard auxiliary units. The heated suit plug-in (A) is mounted on the right side of the controller housing. The interphone jacks (B), for connecting your earphones and throat microphone, lead right out of the controller housing. The interphone selector switch is mounted on the fuselage near your turret. The trouble light (C) is on the front left-hand corner of the controller housing.

The Bendix Upper's manual system can be used only for moving the turret to make repairs and adjustments: it is not designed for operating the turret in combat emergencies. A single crank with a flexible shaft, stored at the base of the turret, is used to move the turret in either azimuth or elevation. To move the guns up or down, put the crank on the elevation shaft (D) in front of the sight cradle. To rotate the turret, you will have to get down in the turret and put the crank on the pinion shaft (E) in the azimuth gearing at the base of the main support column.

Auxiliary units on turret



Getting Out
Before leaving the turret, move it to stowing position—guns pointing straight back toward the tail. Turn off all the switches. Then slide down off the seat and back out of the turret. Once you are out, unlatch and stow the seat.

Preparing the Turret For Combat
The preceding pages have illustrated how to get into the Bendix Upper, operate it, and how to get out again. With this information, you could easily take over the turret In combat.

If you specialize in the Bendix, however, you will have to adjust the sight and guns for a mission, and load ammunition. The method of getting the turret ready for action is explained on the following pages.

Adjusting the Sight

The Bendix Upper s N-8 or N-6A sight fits into a bracket in the sight cradle directly in front of you. To adjust the position of the sight, as may sometimes be necessary in harmonizing the guns, loosen the mounting bolts and turn the adjusting bolts you will find nearby. The two mounting bolts directly in front (A) hold the sight vertically in its bracket; the adjusting bolt(B) directly beneath them moves the sight up or down. The two mounting bolts at the top (C) hold the sight in place laterally; the adjusting bolt (D) in front of them moves the sight from side to side.
For full instructions on care and checking of the sight, see the Sights and Sighting section.
Adjusting the sight sight.



Left and right cartridge belt feeds

Adjusting the Guns
The guns are mounted in the Bendix Upper to feed from the inside—the right gun feeds from the left and the left gun from the right. Each gun is held in its cradle by a front gun yoke and rear bracket. The front is held by two studs that must be safety wired. A recoil guide stud, bolted to the rear of the gun, fits into a hole in the rear mounting bracket, held underneath by an elastic stop nut.

Ammunition feeds

Adjusting locking screws

Loosening rear munt elastic stop nut

Lateral adjustment screw

Special charging units (E) operated by your footrests, are mounted on the outside of the guns' receivers; their mounting bolts must be safety wired. Special case ejection chutes are installed on the outside of the guns to carry used links away from the guns; the hollow pins holding the chutes in the guns must have cotter pins. Special ammunition feed rollers (B) are mounted on top of each gun and held by the gun cover pin, which must have a cotter key.
The guns are adjusted up, down, or sideways in their cradles by means of two Allen adjusting screws in each rear mount, held by two rear and four front mount lock screws.

To make the adjustment:
1 Loosen the rear mount elastic stop nut (D), the two rear Allen lock screws (F), and four front lock screws (A) with an Allen wrench.
2 Turn the bottom vertical adjustment screw (C) with the Allen wrench right or left to move the rear of the gun up or down.
3 Turn the inside rear lateral adjustment screw (G) right or left to move the rear of the gun from side to side.
4 Tighten the rear elastic stop nut and all lock screws, front and rear.
By means of these adjustments the guns can be centered in their mounts. Turn the adjustment screws to the centers of their vertical and lateral adjustments.




Harmonizing the Guns and Sight

There are a number of ways to harmonize the sight and guns in the Bendix Upper Deck Turret. The exact procedure will be defined by the Squadron Gunnery Officer. A handy method is to line up the sight and boresight the guns on some small object such as a tree or chimney, at least 1,000 yards away. You will need an assistant in the turret and a muzzle-type boresight tool to do this.

FIRST, have your assistant move the turret until the dot of the sight is centered on the object. Place the boresight tool in one gun, and have your assistant adjust its rear mount until the same object is exactly centered in the gun bore. Then do the same for the other gun. Sometimes there may not be enough adjustment in the gun mounts. In that case, center the guns in their mounts and boresight each gun on the object. Then move the sight by its adjustment bolts until the dot is on the same object. I

IMPORTANT: Check harmonization by swinging the turret on another small object off to one side, 1,000 yards away, and bore-sighting to make sure sight and guns all line up on the same object. Select another object and check again. If sight and guns are out of line on any object, call in turret maintenance.

Illustration of gun harmonizing
Another method of harmonizing the Bendix Upper is to boresight on a pattern stand, such as the one illustrated here. Set up the stand level with the guns at least 50 yards away. Center the guns in their mounts. Then boresight the guns on the pattern and line up the sight on the sight cross, using the standard technique described in the Sights and Sighting section. Both methods described here are parallel harmonization.
Boreshight templete



Loading Ammunition
Overhead view of ammunition boxes
Two big ammunition cans, one marked for the hang down on either side of the center column, right gun and the other for the left, hold about Load them in the standard fold-in pattern, 400 rounds apiece. They hook on the inside of single-link end first, making sure the rounds will the big ring casting circling your head and point toward the center of the turret when the
Hanging an ammunition canPushing pin in



cans are hung up on the inner rim of the turret. Place the loaded cans on the turret floor, right below where they will hang. Then lift each can straight up, using one knee as a support under the can. On the top edge of each can is a bar which must hook into the support hook on the front of the main turret casting.
At the bottom rear of each can is a bar which fits into a bracket on the controller housing, held there by latch pin. Push the pin all the way in, then give it a quarter turn to lock it.
After the cans are securely in place, pull the double-link end of each ammunition belt over the top of the ammunition rollers, keeping the cartridge points toward the small ends of the rollers. Pull the belt over the top of the cone feed rollers. Then, twisting the belts slightly, bring them up around the guide rollers. Force the first rounds into the feedways.

Two spent round bags, to receive used brass ejected from the guns, hook to the mouth of the guns' case ejection chutes.

Pulling ammunition belt over rollers



Pre-Flight Routine


PBJ airpane
1. Make sure the gun bolts are properly assembled, one for left-hand feed in the right gun, the other for right-hand feed in the left gun. Then install the bolt, barrel, oil buffer, and backplate groups in both guns.
2.. Try to rock the guns in their cradles to make sure they are securely mounted. Check the front and rear studs and mounting bolts to make sure that they are properly safety wired and tight.
3. Inspect the charging units to make sure that they are securely mounted and safety wired.
4. Inspect the ammunition rollers and case ejection chutes to make sure they are properly mounted and the pins holding them have cotter pins and keys.
5. Check harmonization with a boresight tool by boresighting the sight and guns on some small object at least 1,000 yards away, or on a pattern stand. Double-check by bore-sighting on two or three other objects.
6. Inspect the electric cables. Make sure all cannon plug connections are tight. Report any frayed or damaged cables. Take particular note of the interphone cable on the right side of the controller housing to make sure it is not loose or frayed.
7. Inspect your ammunition belts to make sure the rounds are in good condition and properly belted.
8. Load the ammunition cans and lift them into place in the turret. Make sure the cans are hooked up securely in front, and the

latch pins are locked at the bottom rear of the cans. Open the inspection doors in the front of the cans to see that the ammunition is correctly placed in the cans, with the cartridge points facing toward the center of the turret.
9. Pull the ammunition belts up over the lead rollers, then over the cone rollers, and twist them slightly over the guide rollers leading up to the guns' feedways. Don't insert the first rounds in the feedways as yet.
10. Adjust the footrests, if necessary, and raise the seat if you wish—making sure that the seat is securely latched up in place. Get into the turret.
11. Make sure the dome is clean.
12. Reach out to the left wall of the fuselage and turn on the main power switch and heat-light switch.
13. Turn on the sight rheostat and turn it from dim to bright to adjust the brightness of the light and make sure it is working properly. Flip the sight filament switch to both positions to make sure both filaments in the sight bulb are working. If either filament is burned out, replace the bulb. Make sure the optic head is clean.
14. Make sure there is no ammunition in the gun chambers. Charge the guns by lifting up and stepping down sharply on the footrest. Check the guns' headspace. Then test your triggers by pulling one at a time, charging the guns each time and checking the adjustment of the electric



triggers. Listen for a "click" as the firing pins in the guns release. Both guns should fire from either trigger.
15. Run the turret under power in azimuth and elevation at normal speed and then with the high speed button held down, to check on ease of operation. Make sure the turret runs with either safety switch held down. Test the limit stops (called brakes on the Bendix) by attempting to bring the guns down on the fuselage forward and backward. Then stop the turret suddenly and check for creep.
15. Check the fire cutoff system by swinging the turret and guns on the tail and propeller areas of the plane, charging and attempting to fire the guns on each area. Make sure the guns stop firing with the proper amount of safety margin around all sides of the restricted areas—your crew chief will tell you how much.

17. Plug in your headphones and microphone to test whether your crew mates can hear you and you can hear them.
15. Plug in and test your heated suit and the rheostat. Make sure the rheostat controls the amount of heat by turning it to various positions on the dial.
19. Make sure your trouble light operates. Flip on the switch. Pull the light out on its cord all the way to make sure the retractable reel is working properly.
20. Make a final visual check of the turret, inside and out.
21. Just before takeoff, press the first rounds of the ammunition belts into the guns' feed-ways over the belt holding pawls. In flight, charge both guns on the order of the flight commander.


PBJ airplane
1. Run the turret to its stowing position—guns level and pointing straight back on the tail.
2. Clear the guns by opening the gun covers and then charging them twice.
3. Shut off all switches.
4. Remove ammunition from the feedways and all ammunition from the turret.
5. Remove and empty the bags which receive spent rcunds and links from the case ejection chutes.

6. Field strip the guns.
7. Clean and inspect the gun casing groups, following the procedure outlined under the post-flight check in the Guns section of this manual.
8. Detail strip the parts remoyed from the guns, cleaning them and making a thorough check on their condition, as outlined in the Guns section.
9. Report any malfunctions of turret or guns noted on the mission.



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Transcribed and formatted by Thomas Wildenberg for the HyperWar Foundation