You will probably go often on missions where you will have the opportunity to strafe grounded planes, troops, ships or enemy installations. Your training in Position Firing will help you get the proper deflection. The principles for strafing are the same fundamental ones that you use in firing at a fighter in a pursuit curve attack. That point was brought out at the start of the section on Position Firing.


1 Always aim between the attacking fighter and the tail of your own bomber along the line of apparent motion.

In strafing you also aim behind the target to allow for the effect of the motion of your own plane on your bullet. The picture of the newsboy in the Position Firing section illustrated this point. Just remember that in strafing, as well as in firing at an enemy plane in a pursuit curve attack, the deflection is still always applied toward your tail.

TBFs strafing a  coastal installation



2 Use the right amount of deflection.
Your study of Position Firing will drill into you the correct Position Firing deflections for your own bomber's speed. When strafing, always allow a little bit more, usually not more than an additional Vi a rod at 90° and less than that for the smaller angles off, than you use in a pursuit curve attack. That is because of the slight difference between firing at a fighter in a pursuit curve attack and firing at a stationary target.

3 Change the deflection during the attack.
In strafing you also change your deflection according to the angle-off of the target. When strafing, it sometimes will be possible to see where your bullets are hitting. This will aid you in correcting and changing your deflection, but use the basic rules of Position Firing as the primary method of determining deflection.

Strafing a ship

The fact that Position Firing principles apply whether your plane flies a curved course or not is a great help in strafing. Even if your pilot flies a curved course around your target, your correct deflection is based on your own speed and the target's angle-off.





Position Firing has been emphasized in this manual because it is considered the best sighting method for the most dangerous firing situation you will face; namely, the pursuit curve attack. It "works" whether your pilot flies a straight or curved course when under attack. Furthermore, as has been said, the principles of Position Firing can be used in strafing. Important practice in Position Firing will be gained on the 3A-2 Trainer/ which is the best ground device so far developed for aerial free gunnery sighting training. Gunners returning from combat say their work on the 3A-2 trainer was a great help in preparation for combat gunnery. Make the best use of your time in the 3A-2 rooms.
Sighting practice, however, is not limited to the 3A-2. It can also be gained on your gunnery school machine gun ranges. It is difficult to simulate a pursuit curve attack on the railroad and towed sleeve ranges. These ranges do, however, give you practice in applying deflection on a moving target. On these ranges you should use another sighting method that is also a part of your free gunnery knowledge—namely, the 2/3 OF A SECOND METHOD. This is a LINE OF APPARENT MOTION method of sighting. You have already learned about the "line of apparent motion" in Position Firing. If you use the 2/3 of a Second Method on your gunnery school ranges you will be better able to handle firing situations in the air that cannot be handled by Position Firing-situations, for example, where a predetermined deflection will not apply. A .30-caliber bullet travels about 1800 feet in 2/3 of a second.



The main principle of the 2/3 of a Second Method is that it takes a bullet about % of a second to get out to 1800 feet, a good average in-range firing distance, and a good range for your railroad targets. If you can estimate the distance that the moving target will move in % of a second, you can give the target the proper amount of deflection and get hits. A way to get the right amount of deflection on a target moving parallel to you at a range of 1800 feet is given in the three steps below: Target moving illustration

1 Center the target in your ring sight at 1800 feet.

2 "Freeze" your gun and say out loud a word such as "elephant." (It has been found that saying a three syllable word takes about 2/3 of a second.) Note the target's line of apparent motion and how far it moves across your ring sight in 2/3 of a second while saying "elephant."

3 Place the target in the same corresponding position on the opposite side of your ring sight and open fire. You are now applying the proper deflection along the target's line of apparent motion.

If your target range is 1200 feet you should say a two syllable word such as "Japan" rather than "elephant." If the range is 600 feet you should say "Jap." After enough practice with these steps you should be able to estimate the deflection for your moving target ranges without having to follow the full routine. But use the method at the start. Find out your own deflections on your railroad ranges by this method. With sufficient practice you will learn to determine the correct point of aim without stopping to think about it.







Using proper deflection

                 .     . . . . Target only in motion

1800 ftTarget in center of sightDetermioning proper deflection
 1 Place target in center of sight2 "Freeze" gun and note direction and distance target moves in 2/3 of a second3 Then place the target the same distance on the opposite side of the ring sight and fire.



. . . . Target and Gun motion

Target and gun moving at same speed


So far, discussion has been directed toward the use of the 2/3 of a Second Method on the moving target-fixed base machine gun range (the target is moving, you're standing still). When it is used on a moving target-moving base machine gun range (the target moves and so do you), the situation is closer to what it will be in the air. By giving motion to your own shooting base, the real importance of the target's LINE OF APPARENT MOTION becomes evident.



In the following cases, deflection is determined by the targets apparent motion.





Freeze gun on target and
note that there is no ap-
parent motion in 2/3 of a

No apparent motion of target


Center sight on target (for
all intents and purposes a
no defection shot) . . . . .
and fire.





Determine line of appar-
ent motion by freezing
gun and note distance tar-
get moves on line in 2/3 of
a second.

Showing apparent motion of target and amount of deflection


Place target on opposite
side of center of sight an
equal distance on line of
apparent motion and ...





Determine line of appar-
ent motion by freezing
gun and note distance tar-
get moves on line in 2/3 of
a second.

Apparent motion and deflection are opposite than above


Place target on opposite
side of center of sight an
equal distance on line of
apparent motion and ...



The same picture is present in the air. Assume that you are flying parallel to an enemy bomber. If the enemy is moving faster than you are, he will move forward in your ring sight. If he is moving slower than you are, he will move backward in your ring sight. In the air, the line of apparent motion may be in any direction—forward, back, up or down. As on the ground, you will find that when you fly a straight course, the deflection will always be applied along the target's line of apparent motion !n air firing, at any but close ranges, a slight allowance for bullet slowdown will have to be made.
As illustrated in the examples above, the apparent motion may be in any direction. Through your training in the 2/3 of a second method, you can determine the line of apparent motion and the amount of deflection.
In Position Firing, deflections can be figured out ahead of time, based on the speed of your own plane. This is possible because a fighter plane trying to hit you usually flies a set track known as a Pursuit Curve. The fighter is limited by his fixed guns. However, oftentimes while on patrol you may come in contact with enemy bombers. On some occasions you may attack those planes; on other occasions, they may attack you. When they attack, the course they can fly is not limited by fixed guns. They will also have free guns and possibly turrets. The rules of Position Firing cannot ordinarily be used against this type of attack, but the principles of the "LINE OF APPARENT MOTION" METHOD OF SIGHTING learned on your gunnery school ranges through the use of the % of a Second Method can. Whenever you have a duel with an enemy bomber, while flying a STRAIGHT course, you can use the fundamentals of the 2/3 of a Second Method, learned on your gunnery school machine gun ranges.




Tracer can be of help to you in sighting, but it also can play many false tricks unless you understand its behavior. The main point to remember about tracer is—never use it as the sole means of sighting. When you use it, it should be used in connection with your ring sight and your regular sighting method.

Tracer bullets actually do not curve any more than any other kind of bullet, but when "fired from a moving gun they appear to have what is called "CUT BACK." "Out back" is what a stream of water appears to do when you swing a garden hose. When you swing your guns, the trace also appears to "cut back." The faster you swing your guns, the greater the "cut back." This effect will often make you think you are hitting the target when actually you are not. This is particularly true if you watch the whole tracer path, but if you watch the trace through your ring sight at the target, tracer can help. It can help you keep on the target's line of apparent The Garden Hose motion. It can help you correct your deflection, if you watch the trace at the target. If the trace appears between you and the target, you are not giving enough deflection. On the other hand, if the target appears between you and the trace, you are giving too much deflection.

Garden Hose effect

Again—to use tracer properly, use your regular sighting method to determine deflection; then watch the trace at the target through your ring sight.

Squadron doctrine will determine whether you have tracer belted in your ammunition and how it will be belted. When you have it, remember that tracer alone is not to be used as a sighting method. However, tracer can be a supplement to your regular sighting method, if properly used.




Every gun you will use in combat, regardless of its construction, is equipped with some type of gun sight. The sight in your gun is a ring sight. It is designed to do two jobs. It can tell you, in the first place, when a fighter is in range, and in the second place, where to aim your gun to knock down that fighter.


To help you estimate range and apply the deflections required for Position Firing, your ring sights should have rods that are of a convenient size for range estimation, as well as of a standard size for Position Firing deflections.

Illustration showing relationship between mil angle and rads
One foot rule
Rods are based on mils. A mil is a unit of measurement for very small angles. One gunnery mil is the angle formed at the eye when viewing a one foot object at 1000 feet.
One rad

A 35 mil angle measures off 35 feet at 1000 feet. One rod of your sight is 35 mils. Therefore, a 1 rod deflection must offset the gun barrel at an angle of 35 mils. A 2 rod deflection must offset the gun at an angle of 70 mils, and a 3 rod deflection must offset it at an angle of 105 mils. The standard rods deflections given in the section on Position Firing apply only when 1 rod of a sight is equal to 35 mils. Thus, the inner ring of all ring sights must have a radius which will give a 35 mil angle.



Although the caliber .50 BAM gun is the gun that the great majority of you will use, the illustrations for iron sights are made with the caliber .30 gun because iron sights are more frequently used with this gun.



Ring sight on .30 caliber maching gunRing sight on .30 caliber maching gun
a Mk 13 ring sight and a Mk 7 post mounted on a cal. 30 B.A.M. gun

The simplest of all aerial gun sights is the iron sight— a metal ring or set of rings at the rear of the gun and a metal post topped by a bead or small ring at the front.
By lining up the center of the rear ring sight and the center of the bead or ring on the front post, your guns will fire in the direction you want them to fire. If your sights are not lined up, you will not get hits. Another important rule that you must remember when using iron sights is to keep your eye the proper distance behind the rear ring at all times. The distance between your eye and the ring is called your sight base.

Look through a 35 mil iron ring sight using the proper sight base. A 35 foot plane at 1000 feet fills exactly one rod of your iron ring sight.

Right way to correct sight base
Now move your eye back from the correct sight base and the plane fills more than one rod. The sight has become less than a 35 mil sight because you have lengthened your sight base.
Wrong way to correct sight base
Next move your eye closer than the correct sight base and the plane fills less than one rod. The sight is now more than a 35 mil sight because you have shortened your sight base.
wrong way to correct sight base
A correct sight base is therefore essential to keeping your iron sight a 35 mil sight.



The correct sight base varies with the actual size of the ring sight itself. Below are shown a number of correct sight bases for 35 mil sights of various sizes.
Sight bases varying with sight ring size.

While all of these ring sights are of different sizes, their sight bases have been so adjusted that they are all 35 mil sights. Proper sight bases are given for each 35 mil iron sight in the Aviation Ordnance Equipment Catalogue.

However, if you are ever in doubt as to whether you have a 35 mil sight or not, place a board 31/2 feet long at a right angle to the eye and 100 feet away. Line up your ring sight on the board, and if the board fills 1 rod of your sight you know that you have a 35 mil sight.

Sight base useing 3 1/2 inch board.

To sum up, maintaining the correct sight base with a 35 mil iron sight is
essential for:

1 Proper range estimation. Remember the single engine fighter fills 1/3 of a rod of your 35 mil sight at 3000 feet, the in-range firing distance for bow attacks, and Vi of a rod at 2000 feet, the in-range firing distance for other attacks. The twin engine fighter fills Vi rod at 3000 feet and 3/4 rod at 2000 feet.

2 Proper use of Position Firing Deflections. Your deflections are given in terms of rods of 35 mils. When applying the deflection with an iron sight, keep the proper sight base and apply the proper number of rods deflection toward your own bomber's tail.



The 35 mil iron sights that you may use are shown below.


Ring sight chart.></td></tr> 
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One great advantage of iron sights is that they seldom get out of order unless the metal is bent, broken, or rusted through. They need only be checked for these defects which can be seen at a glance. The only care they require is occasional oiling to prevent rust and to make the mounting adjustments operate easily.




Mark 9 sightTHE MARK 9 or two-ring reflector sight, is a simple arrangement of a single electric light bulb inside a small housing, a reticle, lens and reflector plate. You use the sight by looking at your target through a glass plate on which the light bulb projects the dot called a "pipper," and two rings which show you where to aim. The pipper shows exactly where your guns are pointed; in applying Rule 1 of Position Firing, you place the pipper between the attacking fighter and the tail of your bomber, along the fighter's line of apparent motion. To apply any deflection up to two rods, simply place the fighter on the appropriate place as shown in the diagrams in the section on Position Firing. To apply deflections greater than two rods, simply imagine additional rings outside of the two rings and the same distance apart as the 35 mil ring and the 70 mil ring. Then place the fighter with reference to the appropriate imaginary ring as shown in the diagrams in the section on Position Firing. With reflector sights there is no problem of lining up the bead and peep and the optical system makes it unnecessary to keep a set sight base. Each rod is always equal to a 35 mil angle, even if you move your head as you look into the sight. Use and care of the Mark 9 sight are extremely simple. Your chief job is to make sure that the sight is in working condition before each mission.

Using the Mark 9 Sights On the side of the case is a knurled thumb screw switch which can be turned to "off," "Night," or "Day" to allow varying degrees of light. A 21-6 candle power double filament, double contact, type S8, 24-28 volt inside frosted lamp bulb is used in the sight. The lamp bulb has a line on one side of its base. The lamp socket in the sight has a white line on one side of it. The lamp bulb must be placed in the lamp socket so that the mark on the base of the lamp bulb lines up with the white line on the lamp socket in the sight.


Be sure to line up index mark on bulb and socket

Installing bulb



If the lamp is installed so that these two lines do not "line up" a coil in the sight will burn out and the lamp will not light. To change lamp bulbs, pull off the side of the lamp housing by pressing up on the button on the bottom of the sight. Replace the bulb as soon as possible after one filament burns out—or in any case after every third mission. Always carry a spare bulb.

In front of the hooded section is a sun filter which may be positioned in or out of the line of sight by a scalloped thumb wheel. Always use the filter when firing into the sun. Keep fingerprints, grease, oil and dirt off the exposed glass parts. If the exposed glass parts get dirty, clean with liquid lens cleaner and a clean chamois or piece of soft tissue paper.

Exploded view Mark 9 Sight

Pre-Flight Check.
1. Make sure that the reflector plate is clean.
2. Test the knurled thumb screw switch to make sure that both filaments work and that the dimmer works properly.
3. Make sure that the rings and pipper look sharp and clear.
4. Center the sight on some distant object and then move your head from side to side. The rings and pipper should stay right on the object. If they move away or if they appear fuzzy, the sight needs adjustment.
5. Make sure that you have at least one new spare bulb.

THE MARK 9 Mod 1 SIGHT The Mark 9 Mod 1 sight is identical with the Mark 9 except that it operates on 12 volts. The Mark 9 operates on 24 to 28 volts. If the electrical system of your airplane has an output of 24 to 28 volts you will use the Mk 9 sight. If the electrical system of your airplane has an output of 12 volts you will use the Mk 9 Mod 1 sight. The Mk 9 Mod 1 uses a 21-6 candle power, double filament, double contact, type S8, 12 volt inside frosted lamp. The line of the base of the lamp base must be lined up with the white line on the lamp socket the same as in the Mk 9. Everything stated above with reference to the Mk 9 applies equally to the Mk 9 Mod 1 except as to the voltage.





Automatic computing sights are one of the new developments of air warfare. These sights serve as mechanical brains in helping the gunner shoot down enemy planes. They do this by calculating the needed deflections and making it simple for the gunner to apply them. They are completely different—in construction, operation, and use—from ring sights. With a computing sight you do not need to apply the rules of Position Firing and range estimation. Instead you must learn a new mechanical technique of aiming. And you will need plenty of practice—for unless you use a computing sight properly, the sight will not calculate deflections accurately.

The descriptions of automatic sights in the following pages are confined to operational information which you need to knock down planes. You will not be concerned with how the mechanisms work, for only trained technicians should make adjustments or repairs.


K-4 gun sight.

The Sperry K-4, mounted in the Sperry Lower Ball turret, is used by sighting through a glass screen mounted in an optic head—just as you look into a reflector sight. Visible in the K-4's glass screen are three lines called reticles — one horizontal and two vertical. These reticles are used, instead of a ring, to line up the target. Connected with the optic head is a computing



unit which contains all the mechanism for calculating deflections and offsetting the guns to the proper angle.

To make its computations, the sight requires three specific items of information about the enemy fighter:

The target dimension, which you supply by setting a target dimension dial on the sight housing to the wingspan of the target plane.
2 The range of the fighter, which you supply by adjusting the range control—a pedal which you operate with your left foot—to keep the vertical reticles framing the target
3 The apparent motion of the target, which you supply by tracking the enemy plane so that the horizontal reticle is always across the center of the target.

Given this information, the K-4 makes computations which increase the effective range of
your guns to 3,000 feet.

To use the K-4:
Turn on the sight switch, which is on the front panel of the sight housing. This will light the reticles and turn on the computing unit. Use the rheostat on the sight housing to adjust the reticles to the proper brightness. Adjust the filter for proper contrast.
2 As soon as you see an enemy fighter, determine what type of plane it is, recall the wingspan for that type, and set the target dimension dial.
3 Track the enemy fighter by moving your guns to keep the horizontal reticle right across the center of the fighter.

Adjusting range control

4 Keep moving the range control to make the vertical reticles frame the width of the fighter's wingtips. By turning the range control, you can move the reticles closer together or farther apart. By keeping the reticles right on the width of the fighter's wingtips, you enable the sight to make a sufficiently accurate estimation of his range. If the fighter is banked, an imaginary circle through his wingtips should be framed by the vertical reticles. If you see the top or bottom of the fighter instead of the nose, an imaginary circle through the wingtips should be framed by the reticles. Targets seen from the side present a special problem. On most planes, wingspan and length are nearly the same; ranging will

Targets as seen from varioius aspects





be sufficiently accurate if you frame the fuselage or an imaginary circle drawn through the ends of the fuselage. But if you know that the wingspan is considerably longer than the fuselage, keep the reticles a corresponding distance from the ends of the fuselage. The target dimension dial registers only up to 60 feet. For the very few enemy planes which have a wingspan over 60 feet, set the dial at half the wingspan and frame the center half of the plane only.

5 Fire at the enemy—using bursts of the length found most effective in your combat theater—as long as he is within range. When you have set the target dimension dial for the wingspan of the enemy plane he will be in range when he just fills the smallest possible reticle opening.
6 Track the target as smoothly as possible The sight can work effectively only if you give it a clear, smooth picture of the fighter's apparent motion. Its computations require a little time; your aim will not be correct if you fire without tracking smoothly. This is not too easy and takes a lot of practice.

Care of the K-4
Avoid bumping or jarring the delicate optic head. Don't touch it except to clean the reflection glass, dust shield, and sun filter. Never try to oil or adjust the sight yourself. Never operate the turret unless the sight switch is on—or you will ruin the computing mechanism.
Never turn on the sight switch before the turret's main power switch has been turned on.

Pre-flight Check
1 Before starting on a mission, turn on the sight switch and make sure that the reticles light, and that the rheostat works properly.
2 Move the guns and track to the left, right, up, and down. The reticles should lag a little, moving across the optic head in the opposite direction.
3 Make sure the vertical reticles move closer together and farther apart as you turn the • range control.

The Sperry K-3 is the original computing sight developed and was designed for the Sperry Upper Turret. The K-4 is actually an upside down version of the K-3. The range control for the K-3 is a thumb knob or motorcycle type handgrip on the turret control handle. In all other respects, the K-3 and K-4 are exactly alike




No sight can do its job accurately unless it is properly lined up with the bore of the gun. The sight and gun must work together; the technique of making them work together is called boresighting.

Boresighting does one thing. It lines up the sight and gun so that you can look through the sight and know where your gun is pointing.

Before you fire a gun you have never used before, be sure it is correctly boresighted. All guns should be checked constantly for boresighting—before each mission in combat zones. All guns, whether hand-held or mounted in turrets, and all sights, whether iron, reflector, or computing are boresighted in the same basic way. In the pages that follow, boresighting of iron sights and handheld guns will be discussed. In the turret section, a more detailed discussion of boresighting turret guns will be given. With turrets you will usually be dealing with more than one gun. Boresighting of multiple gun installations is called harmonization.

To understand boresighting you must understand two definitions: sight axis and bore axis. The sight axis is the straight line drawn from your eye through the bead and peep and on out into space. With the reflector sight, this line is drawn from your eye through the pipper out into space.

The bore axis is the straight line drawn through the center of the barrel of the gun and on out into space.

Boresighting establishes a relationship between these lines, so that you can aim your gun accurately. Squadron doctrine will decide how those two lines are to be set. They may be made to run

Sigth axis and bore axis
parallel; they may be made to converge; they may or may not be adjusted so as to allow for the pull of gravity on your bullets. The relationship of those two lines should be set, however, to give the densest pattern to your bullets at a given range. The simplest boresighting will be on your primary machine gun range in gunnery school. There the target will be about 100 feet from you. You don't need to worry about the effect of gravity drop. Your only problem will be to line up the sight axis and bore axis on the same mark on the target. In other words, you want those two lines to converge or come together on the target.



To do that, take the following steps:

1. Place the gun in a mount which will permit you to lock it in position.

2. Loosen the front post sight locking nuts. (If the Mark 9 Reflector sight is used, loosen the sight adjusting nuts on the hood of the sight.)

3. Remove the back plate, bolt, and driving spring assembly.

4. Trip the accelerator forward.

5. Line up the bore axis dead center on the reference mark.

6. Line up the sight axis dead center on the same reference mark.

7. Tighten the front sight locking nuts. (If the Mark 9 sight is used, tighten the sight adjusting nuts on the hood of the sight.)

8. Reassemble the gun.

Short range bore sighting

Your gun is now boresighted for firing at a range of 100 feet.
(If a Mark 1 boresighting kit is used, steps 3, 4, and 8 can be omitted, because the kit contains muzzle and breach adapters which are used with a periscope-like attachment, and which make it unnecessary to sight through the rear of the barrel in order to line up the bore axis.)



For longer ranges, the problem is a little different. The bullet will gradually drop off due to gravity, and the further it goes the more it drops.

If you lined up the sight axis and bore axis on the same mark at 1200 feet, for example— the range at which your guns are boresighted for advanced firing in gunnery schools— your bullets would hit about four feet low at that range. To allow for this, two marks should be on your target—the one for the bore axis to be above the one for the sight axis, if you

Bore sighting with and without gravity
are boresighting your guns at 1200 feet, the marks should be 40" apart for the caliber .50 gun and 48" apart for the caliber .30 gun. Boresighting would then be simple if you had a full 1200 foot range. However, this range is not always available. In that case, you use templates, which are usually figured out by your gunnery officer. A template is a bore-sighting card showing the proper marks on which to line up your bore axis and sight axis, and can be used successfully at short distances. The proper position for the marks are figured out mathematically. However, since any error on your template will be magnified at the full range, be certain the templates are official and correct.
Bore sighting with templete
At gunnery schools a full allowance for gravity drop will be made, because there you are firing on the horizontal. In combat you will not always be firing on the horizontal, which means that there will be a varying effect of gravity drop. In the Fleet, therefore, gravity allowance will be determined by squadron doctrine. You may boresight your guns on a template, or you may merely boresight them on some distant object. The latter method is called infinity boresighting. Boresighting on templates is the general practice on carriers. You will also use templates in gunnery schools. However, for convenience, infinity bore-sighting is often used in land based squadrons. Regardless of what prescribed marks you use, you follow the same procedure as previously outlined and in the exact sequence. The point to remember is to be certain that your guns are boresighted properly according to the method prescribed in your squadron.



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Transcribed and formatted by Thomas Wildenberg for the HyperWar Foundation