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.
YOUR THREE RULES FOR POSITION FIRING.
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.
Use the right amount of deflection.
Change the deflection during the
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.
2/3 OF A SECOND METHOD OF SIGHTING
|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.|Restricted
|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:|
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.
. . . . . Target only in motion
|1 Place target in center of sight||2 "Freeze" gun and note direction and distance target moves in 2/3 of a second||3 Then place the target the same distance on the opposite side of the ring sight and fire.|
. . . . Target and Gun motion
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.
|1||WHEN TARGET IS MOVING AT SAME SPEED AND IN SAME DIRECTION AS YOU ARE . . .|
gun on target and
on target (for
|2||WHEN TARGET IS MOVING FASTER THAN YOU ARE . . .|
line of appar-
|3||WHEN TARGET IS MOVING SLOWER THAN YOU ARE . . .|
line of appar-
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.|
|WHEN AN ENEMY BOMBER IS FLYING IN THE SAME GENERAL DIRECTION OR ON A PARALLEL COURSE AND IS WITHIN RANGE.|
|APPARENT MOTION FROM a TO b. PLACE ENEMY PLANE AT c AND FIRE.|
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.|Restricted
|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.|
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.
35 MIL RAD is THE BASIC MEASURE OF ALL REFLECTOR AND
IRON RING SIGHTS IN CURRENT USE IN NAVAL AVIATION FREE GUNNERY
|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.|
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.|
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.
|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.
|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.|
|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.|
|A correct sight base is therefore essential to keeping your iron sight a 35 mil sight.|Restricted
|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.|
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.
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.
up, maintaining the correct sight base with a 35 mil iron sight is
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.
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 SIGHTS AND CORRECT SIGHT BASE
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.
REFLECTOR RING SIGHTS
|THE 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.
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 differentin construction, operation, and usefrom 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 practicefor 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.
THE SPERRY K-4
The Sperry K-4, mounted in the Sperry Lower Ball turret, is used by sighting through a glass screen mounted in an optic headjust 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:
this information, the K-4 makes computations which increase the effective range
To use the K-4:
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.
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.
of the K-4
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 boresightingbefore 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
|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.|Restricted
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.
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.)|Restricted
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 targetthe one for the bore axis to be above the one for the sight axis, if you
|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.|
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.|Restricted