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.
Facts and Figures
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.
The stowing position is 0° elevation and 0° azimuth, guns pointing straight forward.
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.
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.
OPERATING THE TURRET
. Where to Find the Controls
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).
Flick this to the on position.
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
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
|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.
Emergency ExitIt 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.
Preparing the Turret for
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.
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.|Restricted
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.
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.
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.
|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,|
|allowing 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.|Restricted
. . . FOLLOW STEP BY STEP
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.
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.
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.
The Martine Electric Upper Deck
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.
Facts and Figures
The Martin turret operates on power supplied from the bomber's central electrical system.
The turret can move 360 degreesa full circle in azimuth.
The stowing position for turret and guns is 0 degrees elevation and 180 degrees azimuth-guns pointing straight back toward the tail.
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.
turn on the main power switcha 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
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.
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.|
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.
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 beltand you are ready
|OPERATING THE TURRET|
. . where to find the controls
|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 usea 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.|
|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.|Restricted
|Using the Auxiliary Units|
A Elevation and
azimuth hand cranks (Below Control Unit)
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
will find a demand type regulator for the oxygen system on your right arm restor,
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
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.
Before leaving the turret, move it to stowing positionguns 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.
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 jobadjusting your sight and guns, and loading the ammunition for a missionis explained in the following pages.
Adjusting the SightThe 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
Adjusting the Guns
The guns are mounted in the Martin to feed from the insidethe 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.
To make adjustments
on either gun:
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
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.
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.
. . . FOLLOW STEP BY STEP
Install the barrel and oil buffer groups in the gunsleaving out the bolts
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.
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.
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 marginyour 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.
Plug in your headphones and microphone, to test whether your crew mates
can hear you and you can hear them.
Run the turret to its stowing positionguns 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.
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.