Martin ball turret

Martin Ball Turret
Martin 250SH-1A & 2

The Martin 250SH Ball Turret is found on all Navy flying boats using bow turrets. It is a complete self-contained unit with everything at your finger tips to make it hot for an enemy fighter flying a bow attack on your plane. In addition, you will find those two caliber .50 machine guns mighty efficient in cleaning a gun crew off the deck of a submarine. In this turret the gunner moves with his guns and sight in elevation and azimuth. Its appearance and operation is very similar to the Erco 250SH Turret.
The Martin 250SH Turret has been produced in two models, which are, for the most part, the same; the Martin 250SH-1A used in the bow of the PBM-3D, and the Martin 250SH-2 used in the same position on the PB2Y-3 airplane.

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Facts and Figures

POWER
The Martin 250SH operates hydraulically on pressure built up by a hydraulic pump driven by a constant speed electric motor.

SIGHT
Its sight is a standard Mk 9 reflector sight, fully
described in the introduction to this section.

Elevation limits
Azimuth limits

ELEVATION
Both the Martin 250SH-1A and 250SH-2 turrets can be elevated 87° above the horizontal, and depressed 33° below the horizontal.

ARMOR
The armor plate in the turret protects the gunner from enemy fire in any direction in which he trains his guns. It consists of three groups:5/8" steel armor plate in front of his face, 5/8" steel armor plate to protect the booster motors and ammunition chutes and 1/2" armor plate to protect his body and ammunition boxes.

AZIMUTH
The Martin Ball Turret in its installation in the
PBM-3D and PB2Y-3 has an azimuth motion of
79° either side of the center line of the plane.
STOWING POSITION
The stowing position is 0° elevation and 0° azimuth, guns pointing straight forward.
PBM silouette

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Getting In

Remember, a bow turret is no place to be while landing or taking off. Your weight in the bow puts undue stress on the airplane— besides making the plane unbalanced; therefore, never enter the turret until the plane is in full flight.

Entering the Martin Ball Turret presents little difficulty if you take the following steps. Before you get in, have your flight engineer turn on the bow turret switch on the flight engineer's panel. Outside the turret in a junction box, conveniently located near the turret on a bulkhead, is a red indicator light and a turret switch, which turns the power to the turret on and off. In the turret is a similar switch marked main power with a red indicator light off to the side. Wait until you are in the turret to turn on the current, as the switch on the outside junction box is to be used for emergency purposes only.

Facing forward, enter the turret through the opening in the bottom and reach up, grasping the top of the face armor plate to assist in pulling yourself in. Once inside, reach down on your left side and release the seat lock, allowing the seat to follow the track to its seated position. Seat yourself and look through the sight to determine if you are at the proper height. If not, reach down under the seat with your right hand and grasp the seat-adjustment handle. With your thumb release the catch on the handle freeing the seat, and by moving the seat-adjustment handle up or down the seat will raise or lower. When you are at the proper height, allow the catch to spring back and re-engage; this locks the seat at the height you have selected. Adjust and fasten the safety belt. You will need it in this turret.


Getting into the turret

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Control panel

OPERATING THE TURRET

Pressure gage,  elevation lock handle, and azimuth position lock

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

First of all, check the low pressure gauge, which is located to the side of your right ankle. This gauge should read 25 to 30 lbs. It is very important that this pressure be maintained as it insures smooth operation of the turret

. Unlock the elevation landing lock, which is on the forward left hand side of the ball, by pulling out and rotating the handle up. Then determine if the azimuth position lock, on the lower left hand side, is in the extreme unlocked position. These two operations free the turret.

On your upper right-hand side, you will find the control panel. Click on the main power switch (A), and the red indicator light (B) on the panel will light up as well as the red indicator light on the outside junction box, showing that the power is on in the turret. Located on the bottom of the control box is another switch marked pump motor (C).

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Flick this to the on position.
Lift the little red plastic cover on the control
panel marked gun and sight switch (D) and
raise the switch under it to the on position. The control handles to operate the turret are located in front and above your knees. To start the pump motor, use the bottom edges of your hands to press down the two safety switches. When the motor is running the handles will automatically go to neutral position. For this reason it is best to press the safety switches down before grasping the hand grips of the control handles. If this is done the control handles will move to the neutral position without moving the turret. If the control handles are in any other position than neutral and the safety switches are closed, the turret will start, causing immediate and violent action. Either safety switch will operate the turret.
Depressing the safety switches also turns on the sight and provides power to the booster motors so that they will operate when the guns are fired.
To adjust the brightness of the sight use one hand to hold the control handles, keeping the safety switch depressed, and with the other hand turn the rheostat on the sight. To operate the turret turn the control handles in the direction you desire the turret to move. For azimuth (right or left)—the control handles are operated exactly like those of a bicycle. For elevating the turret move the upper part of the control grips backward; and for depressing the turret move the top portion of the control handles forward. Don't jerk the controls—move them smoothly and deliberately. Right under your index finger on both control handles are the triggers. Either trigger can fire both guns. In front of you on the left is the high pressure gauge. As soon as the pump is operating, the

Control handles,  adusting reotstate, high pressure gauge

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Hydraulic gun charger Hydraulic gun charger control knob
high pressure gauge should register 960 to 1000 lbs. pressure. While operating the turret, from time to time check this gauge to see that proper pressure is maintained.
Next to your left knee is the hydraulic gun charger control knob, which operates the gun chargers located on the outboard side of each gun. To charge the guns turn the control knob
to the Fire position. Depress the control knob sharply. Both guns will be charged at once and ready to fire. If the control knob is turned to the Safe position before depressing, the gun bolts will remain in the retracted position which provides access for removing a jam. Remember, the pump motor must be operating before you can charge the guns.
Using Auxiliary Equipment

The oxygen system of the turret is completely self-contained. It consists of an oxygen cylinder and a regulator valve mounted on the left seat support and a rebreather mounted to the left side of the ammunition boxes in front of you. A spare cannister is mounted on the left side of the ball structure. Plug your heating suit into the utility plug outlet (E) on your control panel and turn on

Regulator valve

the utility switch (F), which is also on the control panel. The interphone jack box is located on the top left side of the ball structure. This is where you plug in your interphone jacks for your head set and throat microphone. On the front side of the box is the push-to-talk button which enables you to talk with your crew mates.

The trouble spotlight is mounted on a rib which is part of the plexiglas dome. A ball-swivel joint enables you to direct the light where you desire. The spotlight switch (G) is found on the control panel.

Provisions have been made for mounting a gun camera below and parallel to the guns just above the ammunition boxes. To put it in

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operation, it is necessary to have the camera switch (H) and the main power switch in on position on the control panel. In addition you must depress either safety switch and either trigger switch.
A hydraulic emergency hand pump is provided to operate the turret in case the pump or the electric power fails. For manual operation hold the left-hand grip of the control handles turned in the desired direction and work the hand pump with your right hand. This hand pump will be of great assistance to you in seating the elevation stowing pin and boresighting the guns when a small amount of carefully controlled movement is desired.
Operating hand crank

Getting Out
In getting out of the turret before landing, it is of the utmost importance that you pursue the following steps carefully:
Move the turret to stowing position—guns at 0° elevation and 0° azimuth and turn off all switches. With the hand pump rock the turret slightly until you can slip the elevation landing lock pin into position. Then reach down on the lower left-hand side of the ball and turn the azimuth position lock to on.
IT IS EXTREMELY NECESSARY THAT THESE LANDING LOCKS BE SECURED. IF THEY ARE NOT, THE TURRET IS LIKELY TO SWING AROUND FREELY IN LANDING, CAUSING DAMAGE TO THE SHIP AND TO ITSELF.
Disconnect all auxiliary units you have been using. Brace yourself against the back of the turret seat rest and lift up on the seat, pushing it back and up, allowing it to follow the seat track until it is in the locked position out of the way.
To get out, all you have to do is grasp the top of the face armor plate and swing down and out of the opening in the bottom of the turret

Getting out of the turret

Emergency Exit

It might be possible that you will want to get out of the turret in a hurry. For such an emergency, an escape hatch is provided in the Plexiglas dome directly above you. Two plastic handles are located on either side of the hatch, and by turning them a quarter turn the hatch will fall inboard. If you stand on the seat you will find it an easy job to crawl out of the top of the turret.
Getting Out Operating hand crank

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Preparing the Turret for Combat
From the preceding information you now know how to get into the turret, operate it, use its auxiliary equipment, and how to get out. But this is not the entire job which will qualify you as a specialist in the Martin 250SH Turrets. You still have to learn how to adjust the guns and sight, harmonize them, and load ammunition. All this will be found in the following pages.

Overhead of ammunition feed
Adjusting the Guns
In the Martin Ball Turret, two caliber .50 machine guns are mounted to feed from the outboard side. The right hand gun feeds from the right and the left hand gun feeds from the left.
Adjusting nuts on front and top and bottom of yokeProvisions are made for adjustment of the guns both up and down and sideways. Vertical adjustment is obtained by nuts provided on the front yoke where it attaches to the front mount support. Jam nuts are provided on both top and bottom so that the yoke can be firmly held in position. Azimuth adjustment is obtained by a coupling located directly under the gun at the rear mount. Turning the hexagon-shaped portion of this assembly results in the gun being shifted sideways. Locking is obtained by forcing the jam nuts against the gun frame.

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The Sight
The Navy Mk 9 sight is mounted between the rear gun mount castings in front of the face armor plate. To adjust the sight, as may be sometimes necessary in harmonizing it with the guns, make your adjustments on the sight head. For instructions in making these adjustments see the section on the Mk 9 sight in the general introduction to this section.
Harmonizing the Guns and Sight

There are a number of ways to harmonize the guns and sight of the Martin Ball 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 from your plane. To do that remove the back plates and bolts from both guns —or use a boresight tool so that you can look through the gun barrels without removing the parts. Turn the turret until the guns point at the object you have selected. Then line up the sight, using the emergency pump to move the turret until the dot of the sight is squarely on the object. Don't move the turret again.
Now boresight through each gun barrel to line up each gun. Adjust each gun by its front and rear mount adjustments until the spot the sight is centered on is exactly in the center of each gun bore.
Sometimes the amount of adjustment in the front and rear mounts of the guns may not be sufficient to bring the guns to bear on the object. In that case boresight each gun on the object selected. Then you must make an adjustment on the sight head to line up the dot on the same object.

 

Boreshight templete

Another method of harmonization is to line up the sight and guns on a special pattern stand or template, such as the one illustrated above. Set up the stand as level as possible at least 50 yards in front of the plane. Center the guns in their mounts. Then boresight each gun on the pattern stand and center the sight on the sight cross—using the standard technique described in the Sights and Sighting Section of this manual. Both methods described here are parallel harmonization.

Illustration of gun harmonizing

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Loading ammunition belts throught the track

Loading Ammunition

Two built-in ammunition magazines holding 400 rounds for each gun are provided in the Martin Hydraulic Bow Turret. They are located in the forward part of the ball in front of you.
1. Remove the pins that secure the two magazine doors and slide them outboard and aft.
2. Load the ammunition belts by flaking them back and forth in the magazine.
3. Lower a wire hook down through each

booster feed into the magazine and attach the hook to the end of the ammunition belt.
1.
When the magazines are full, reinstall the doors, pull the loaded belts up through the booster feeds until one or two rounds of ammunition are engaged in the booster sprockets. Lift the gun covers and pull up enough ammunition to be loaded into the guns. Close the gun covers.

Removal of Empty Cartridge Cases and Links

The empty cartridge cases and links are collected in a chamber located in the front part of the turret between the ammunition box and the ball structure. To remove the empty links and cartridge cases release the catch holding the door at the bottom of the ammunition box,Releasing ammunition door catch
Removing ammunition through access doorallowing the door to fly up. The empty cartridge cases and links will then drop out in the turret. In older model turrets an access door is provided in the outside lower front of the turret ball. After removing the door and cleaning out the ammunition, be sure to secure door.

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Pre-Flight Routine

. . . FOLLOW STEP BY STEP

PBM airplane
1. Check and reinstallall the mechanisms in both guns so they feed left for left gun and right for right gun.
2. Check harmonization by boresighting on a pattern stand or some other object 1000 or more yards away.
3. Try to rock the guns in mounts to make sure they are securely mounted. Check to see if adjustment and jam nuts are safetied.
4. Inspect hydraulic system and lines carefully. This should be done with and without pump operating. If there are any leaks report them immediately. Check filler valve to see that it is in "run" position and safety wired.
5. With the pump in operation operate your gun charger valve knob in both "safe" and "fire" position.
6. . Turn on main power and pump motor switches. Depress safety switches and charge guns. Squeeze either trigger and listen for "click" of firing pins in guns. Test the other trigger by repeating operation.
7. Inspect electrical leads and conduits (Breezes) to determine if they are frayed or damaged.
8. Check all Cannon plugs to see that they are properly seated and screwed up tight.
9. Check oxygen connections to make sure that they are tight.
10. . Make sure Plexiglas dome and escape hatch are properly secured and clean.
11. Check low pressure gauge to determine that you have the 25 to 30 lbs. pressure required.
12. Operate the turret to determine if pressure gauge reads the 960 to 1000 lbs. pressure required.
13. Check for ease of operation in elevation and azimuth.
14. Stop turret with pump running, (control handles in neutral) and check for creep.
15. Check for "line knock" (air in hydraulic system) while operating turret in all extremes. If any is noticeable, report it to maintenance man.
16. Operate the turret to extreme elevation, depression, and azimuth to determine if the limit stops are functioning properly.
17. Turn on sight and gun switch; depress safety switch, and rotate sight rheostat from dim to bright to adjust the reticle to existing light conditions. Make sure the rheostat is working properly. Try both filaments of the sight bulb. If either are burned out, replace the bulb. Make sure the reflector plate of the sight is clean.
18. Plug in your headphones and microphones to test if your crew mates can hear you and you can hear them.
19. Plug in your heating suit and make sure it begins to heat.
20. Make sure trouble spotlight is operating.
21. Inspect all ammunition belts. See that they are in good condition and properly belted.
22. Check booster motors by tipping them toward the guns. Make sure they cut on and off 23. Load ammunition magazines. Feed the double link up over the booster motor sprockets and press the first rounds into the feedway of each gun. You will not charge the guns until you are in the air and so ordered by your plane captain.

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Before Landing
1.
Run turret to its stowing position—zero elevation and zero azimuth, guns pointing straight forward.
2. Engage elevation and azimuth landing locks.
3. Clean the guns by lifting gun covers, removing the ammunition, and charging them twice.
4. Remove ammunition from feedways. Check all switches and make sure they are off.
5. Unfasten safety belt and get out of turret.

PBM in flight

PBM rear quarter

After Landing
1.
Remove all ammunition from chutes and magazines. Open the access door under

ammunition magazines, or the exterior access door in the front lower portion of the ball, and clean out empty links and cartridge cases. Replace access door securely on completing the job.
2. Field strip the guns by removing their working parts.
3.Clean and inspect the gun receivers; then detail strip the parts you have removed from the guns, cleaning them and making a thorough check of their condition. Do not leave excess oil or cleaning fluid in the turret.
4. Report any malfunction of the turret or guns noted on the mission

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Martin electric upper deck turret

The Martine Electric Upper Deck
Martin 250CE-7 through 21

The Martin Electric is one of the most widely used of all turrets. It is designed for quick action and easy operation. It has no gadgets. Everything is made for action and placed where it can be reached quickly when the chips are down.

There are several models. Some of them are improvements over old models, like a new automobile which is better than last year's. Some are simply designed for different kinds of bombers; for example, the model which goes on the PV-1 is not quite the same as the one in the PB4Y-1. But if you can operate one Martin, you can operate them all.

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Facts and Figures

Elevation limits


POWER

The Martin turret operates on power supplied from the bomber's central electrical system.

SIGHT
The turret is equipped with the standard Navy MK 9 reflector sight, fully described in the Sights and Sighting section of this manual.

 

ELEVATION
In elevation, the turret guns can be lowered and raised from a little below horizontal (-6]/2 degrees) to almost straight up (85 degrees).

ARMOR
Armor plate is 1/2 inch thick. It protects the gunner in front, no matter where he aims his guns.

Azimuth limits

PB4Y-2 silouette upper deck turret locations

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

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

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Adjusting footrest

 

Getting In

To start getting acquainted with the Martin Upper, step in. The Martin is easy to get into, simple to operate, and easy to get out of. Only one special precaution is necessary.

Pulling seat bottom drop cableFirst turn on the main power switch—a toggle switch on the fuselage near the turret. Then adjust the footrest to fit your own height. Try it a few times to get the right position.
If you need more room to slip up into the turret, drop the bottom of the seat by pulling on the small cable stretched across the front.
Stoop and squirm up into the middle of the turret, face the front, grasp the two main supports curving about your head, and hoist your body up.

Grasping main supports

Don't pull yourself up by the sight cradle or the two nearby link rods. Your weight on the cradle may throw off the whole sight adjustment, or bend the link rods and throw the sight out of line with the guns.

Finally, stand on the footrest and brace your body against the back of the seat. If you've dropped the seat, use your heel to draw it up until the latches on each side of the seat click. Sit down. Use spare seat cushions to adjust your height until your eye is level with the sight. Snap on the safety belt—and you are ready to go.

Pulling up by sight cradle

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OPERATING THE TURRET

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

Close at hand, as you sit in the Martin Upper, are all the clutches, switches, and controls. They are easy to get at and easy to use—a few clicks and the turret is ready to operate. But be sure to engage the clutches and turn on the switches in the order shown here.
Azimulth clutch, elevation clutch, and master switch

1
Make sure the azimuth clutch is engaged: the small lever, under the control handles and to the right, must be pushed Down. Then make sure the elevation clutch, a lever above the control panel and to the left, is pushed in to the engaged position to the Left.
2
Reach down on the right side of your seat and turn on the master switch. This is like the ignition switch on a car.
ever try to operate without engaging these power clutches. It is like trying to drive your car with the clutch down. You don't get anywhere, and you may wreck the turret.
3
Raise the red plastic cover on the right side of the control panel (opposite page) and flip on the master gun switch (A).
4
Turn the gun selector switch (B) to Both
Guns
. With the switch in this position, both guns will fire when either trigger is pulled. (In the Individual Guns position, each gun is fired only by its own trigger. Use this only when one gun is out of action.)
5
Turn on the sight switch on your sight located in a clamp on the face armor plate. To adjust the brightness of the sight reticle to suit lighting conditions, twist the rheostat button from dim to bright.

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6
Finally, grasp the control handles so that the bottom edges of your hands depress the two safety switches (C). With these switches down, the turret is ready to go. To move the turret, turn the handles just as you would steer a bicycle—to the right to go right, left to go left. Press down on the handles to raise the guns. Pull up on them to lower the guns. The slightest movement of your wrists regulates the turning, raising, or lowering.
The other controls you will need in combat are right at your fingertips. Right under your index finger on both handles are the triggers (D). On the top of the right control handle, by your thumb, is the high speed button (E) that throws the turret into high speed for changing quickly from one target to another. At your left thumb is the push-to-talk-button (F) that opens the interphone system for you to speak. On the main control panel are also reset buttons (G) for the control unit, and booster motor circuits. Down on the front panel of your seat, behind your legs, are resets for the major electrical circuits—auxiliary power, azimuth, elevation, and firing circuits. Depress these reset buttons in emergencies when your power fails.

Gun controls

Gun controls

To charge your guns, pull cross-arm on the charger handles beside your shoulders—grasping the right handle with the left hand, and the left handle with the right hand. Pull them out sharply as far as the charger cables will go. Don't ride the cables on the return action; keep your hold on the handles but allow them to spring back under their own power.

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Using the Auxiliary Units

A Elevation and azimuth hand cranks (Below Control Unit)

Hand cranks

B Heated suit unit
C Interphone jack box and jacks
D
Oxygen regulator and gage (On some turrets, regulator is below control unit, gage on left side)
E Trouble light
Turret with controls indicated
You will find a demand type regulator for the oxygen system on your right arm rest—or, in a few Martin turrets, just below the control unit. The oxygen flow and pressure gage is on the left or right, just off your shoulder.
The source of oxygen supply depends on the plane. In the Liberator the supply is contained in two bottles bolted to the bottom of the seat. In the Marauder the supply comes from the plane's central tanks by tubing which enters a swivel joint in the floor below your turret.
In all Martins the heated suit plug-in is above the left arm rest. The interphone jack box is to the right of your right elbow. The trouble light is at the back of the right arm rest, and the gun camera bracket is just to the left of the sight. Hand cranks for manual operation in emergencies will be found
below and behind the control handles: the right crank for azimuth movement, the left crank for elevation. A trigger switch in the handle of the right crank fires both guns. (Some late models have a foot-firing pedal mounted on the left side of the footrest.)
To change to the manual system: 1) Shut off the turret's master power switch. 2) Engage each crank handle by pulling it from its catch. 3) Hold on to the azimuth handle while disengaging the azimuth power clutch, then to the elevation handle while disengaging the elevation power clutch.
Before going back to power operation, be sure the cranks are disengaged and hooked back up on their catches. If you leave them engaged, they will whirl around and may break your leg.

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Getting Out
Before leaving the turret, move it to stowing position—guns pointing straight back on the tail. Then turn off all the switches. Make sure the azimuth and elevation power clutches are engaged. Disconnect any auxiliary units you have been using. Then brace yourself against the back of the seat and ease your body out of the turret. Drop the seat, if you wish, by pulling its cable.
Preparing the Turret For Combat
With the practical, working information contained in the preceding pages, you could easily take over and operate the Martin in combat. If you specialize in the Martin, however, that will be only part of your job. The rest of your job—adjusting your sight and guns, and loading the ammunition for a mission—is explained in the following pages.
PB-4Y-2 aircraft \

Adjusting the Sight

The Navy Mark 9 sight fits into the gun sight bracket directly behind a 1/2" face armor plate which protects your face. To adjust the sight, as it may be sometimes necessary in harmonizing it with the guns, make the adjustments on the sight head. For full instructions in making these adjustments see the section on the MK 9 sight in the general introduction
MK 9 sight.

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Adjusting the Guns Left and right cartridge belt feeds

The guns are mounted in the Martin to feed from the inside—the right gun feeds from the left and the left gun feeds from the right. The guns are bolted into front and rear mounts in the gun cradles; the two mounting bolts on each gun must have cotter pins. Special charging units are installed on the inside plates of the guns,- their mounting bolts must be safety wired. Special ejection chutes are installed on the outside of the guns to carry links away. The guns may be adjusted up, down, or sideways in their cradles by means of a lock and adjustment nut unit on each rear gun mount.

Adjusting the mounting bolts

To make adjustments on either gun:
1 Loosen the two bottom lock nuts.
2 Turn the elevation adjustment nut left or right to. raise or lower the back of the gun.
3 Turn the eccentric nut left or right to move the back of the gun from side to side.
4 Tighten and safety wire the lock nuts.

By means of these adjustments the guns can be centered in their mounts. Turn the elevation nut until there is a space of about 3/32 inch between the nut and the slide. Then turn the eccentric nut until the thinnest side of its wall faces toward the rear—a mark on the edge of the nut will tell you which is the thinnest side.

Adjusting nuts

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Harmonizing the Guns and Sight

There are a number of ways to harmonize the guns and sight in the Martin 250CE 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 from your plane. Remove the backplates and bolts from both guns, or use a boresight tool so that
you can look through the gun barrels without removing the parts. Turn the turret until the guns point at the object you have selected. Now line up the sight, using the hand cranks to move the turret until the dot of the sight is squarely on the object. Don't move the turret again. Then boresight 'hrough each gun barrel to line up each gun. Adjust each gun by its rear mount adjustment nuts until the spot the sight is centered on is exactly in the center of each gun bore.
Sometimes the amount of adjustment in the rear mounts of the guns may not be enough. In that case, boresight each gun on the small object selected. Then you must make adjustments on the sight head to line up the dot on the same object.

Another method
of harmonization is to line up the sight and guns on a special pattern stand, or template, such as the one illustrated here. Set up the stand as level as possible at least 50 yards from the side of the plane. Center the guns in their mounts. Then boresight each gun on the pattern stand and center the sight on the sight cross, using the standard technique described in the Sights and Sighting section of this manual. Both methods described here are parallel harmonization.

Boreshight templete
Illustration of gun harmonizing

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Loading Ammunition
The Martin carries four ammunition cans, holding about 200 rounds each. When you fold in the ammunition belts, load two cans for the right-hand feed gun by starting with the single-link end at the right edge of the can; the double-lin end will then come out the left side of the can at the top. Load the other two cans for the left-hand feed gun just the opposite.
Loading an ammunition canThe ammunition cans ride on a semi-circular track beneath the guns. Each is held in place by two rollers and a strip which fits into a groove in the track. When you put the cans into the turret, be sure both rollers are in the tracks and the strip is securely in the groove. Load the two right-hand cans into the right track, the left-hand cans into the left track. Push the cans all the way in, so that the automatic latches catch in slots in the cans.
To feed the ammunition belts over the booster motors which help lift them into the guns, you must have two extra 35-round lengths of belt to use as feed strips. Open the hinged sections at the top of the booster chutes. Down each chute drop one of the feed strips — single-link end first — until there are about 10 rounds left between the boosters and the guns. Make sure the rounds rest evenly in the sprocket wheels.
The double-link end of each feed strip goes into the guns' feedways. The single-link ends are connected to the belts in the two inside ammunition cans.
Loading cartridge belt

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Pre-Flight Routine

. . . FOLLOW STEP BY STEP

1. Install the barrel and oil buffer groups in the guns—leaving out the bolts and back-plates.
2. Check harmonization by boresighting the guns on some small object at least 1,000
yards away or on a template.
3. While you are harmonizing the guns, make sure the manual system of operation is working properly.
4. Still using the manual system, check operation of the mechanical limit stops which keep your guns from bumping against the fuselage when pointed toward the side.
5 .Make sure the bolts are assembled properly, to feed from the right on the left gun and from the left on the right gun. Then install the bolts and slide the backplates on both guns.
6. Inspect the ammunition belts to make sure the rounds are in good condition and properly belted.
7. Load the ammunition cans and place them in the turret tracks. Make sure the automatic latches lock them in place.
8. Inspect the electrical cables. Make sure all Cannon plug connections are tight. Report any frayed or damaged cables.
9. Check the oxygen and interphone connections. In some planes this means checking connections to oxygen bottles attached to the seat, and long interphone leads from the wall of the plane. In other bombers it means checking the swivel joint through which both oxygen and interphone lines enter from the floor. Watch for loose connections or failure to swivel.
10. Try to push the turret around by hand to make sure the azimuth clutch is properly engaged. If the turret moves easily the clutch is not properly engaged; push its lever all the way down.

11. Turn on the main power switch. Adjust the footrest and get into the turret. Pull the seat up into place, making sure that both latches on each side catch.
12. Try to push the guns up and down by hand to make sure the elevation clutch is properly engaged. If the guns move easily the clutch is not in place; push its lever all the way to the left.
13. At the same time make sure the gun mounts are secure—you should not be able to rock the guns in their cradles. Make sure cotter pins have been installed in the front and rear mounting bolts.
14.. On the charging units, make sure all three nuts on each charger plate have been safety wired. Make sure the charging cables have been properly attached to their levers.
15. Make sure the dome is clean.
16. Turn on the master switch.
17. Turn on the sight rheostat and turn it from dim to bright to adjust the brightness of light in your sight and to make sure it is working properly. Try both filaments of the sight bulb; if either is burned out, replace the bulb. Make sure the optic head is clean.
18. Turn on the master gun switch.
19. Flip the gun selector switch to Individual Guns. Charge the guns by pulling cross-arm on the gun charger cables. Check the guns' headspace. Then pull one trigger at a time and check the electric triggers for adjust-

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ment—listen for a "click" as the firing pin of the gun releases. Then turn switch to Both Guns and make sure both guns fire properly from either trigger.
20. Test the booster motors by tilting the boosters toward the guns. Make sure the motors cut on and off sharply without lag.
21. 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 operates with either safety switch held down. Test the limit stops which cut off the turret power to prevent the guns from striking the fuselage when pointed forward or backward. Then stop the turret and check for creep.
22. Check the fire cutoff system by swinging the turret and guns to the tail section of your bomber and attempting to fire. Make sure the guns cut off with the proper amount of margin—your crew chief will tell you how much.
23. Put on your oxygen mask, connect it, and make sure you are getting a flow of oxygen. Check the gage to make sure there is proper pressure in the tanks, as determined by your crew chief.

24. Plug in your headphones and microphone, to test whether your crew mates can hear you and you can hear them.
25. Plug in and test your heated suit and the rheostat.
26. Make sure your trouble light operates. Flip the switch to make sure the bulb lights. Pull the light out on its cord to make sure the retractable reel is working properly.
27. Turn off all switches. Drop two 35-round feed strips of ammunition down the booster chutes, leaving about 10 rounds extending from the booster sprocket wheels to the guns. Make sure the rounds rest evenly in the sprockets. Connect the feed strips to the belts in the inner cans, making sure the connecting rounds are pushed in evenly.
28. Make a last visual check of the whole turret, inside and out.
29. Just before the takeoff, push the first rounds of ammunition into the guns' feedways over the belt holding pawl. In flight, charge both guns on order of the flight commander.

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Post-Flight

1. Run the turret to its stowing position—guns pointing straight back toward the tail. Make sure both power clutches are still in their engaged position.
2. Remove the ammunition belts from the feed-ways.
3. Clear the guns by opening the gun covers and hand charging them twice.
4. Take the ammunition cans out of the turret.
5. Field strip the guns.
6. Clean up all brass and links around the deck near the turret.

7. Clean the gun casing groups, thoroughly inspecting the condition of their parts — as described in the post-flight check in the Guns section of this manual.
8. Then detail strip the parts you have removed from the guns, cleaning them and making a thorough check on their condition—also described under the post-flight check 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