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The Waller Flexible Gunnery Trainer
Presented Oct 15, 1945, at the technical conference in New
The 70mm Newsletter
by: Fred Waller, Vitarama Corporation, Huntington Station, N.Y.
729 Seventh Avenue
New York, NY
Phone Bryant 9-6745-6746
Cable: Century New York
The Waller Gunnery Trainer described in this reprint from the Journal of the
Society of Motion Picture Engineers was one of the top secret developments
of the war and was on the restricted list of equipment.
Each Trainer employed nine Century mechanisms operating in synchronism. Five
were used for picture projection and four for the scoring mechanisms or
registers (See Page 86).
Century Projector Corporation cooperated in the
development of this equipment as well as its manufacture. The first
installation was made at Pearl Harbor soon after we were attacked
[7 December 1941, ed].
The operating record established by this equipment is remarkable and
unparalleled in the history of motion picture projection. Operating
twenty-four hours per day, seven days a week, and training more than
1,000,000 men, not a single mechanism failed in service to be returned to
the factory for overhaul.
The Trainer was used by the U. S. Army Air Corps, U. S. Navy. and the
British for the final training and retraining of machine gunners. It was
declared "Essential to Winning the War". Preliminary training was
obtained on less complicated and less accurate devices. It has been
calculated that each trainer paid for itself over - two days of operation
and thus saved many millions of dollars in war cost, plus the more
important saving in men and planes which never can be properly estimated.
The experience gained from this service record is now reflected in better,
more sturdy Century projector mechanisms which are identical in essential
operating features with those used on the Waller Trainer.
Century model "C"
and model "CC" projector mechanisms for regular theatres are available in
all countries of the world, except Canada and the United States, through Westrex Corporation. In Canada they are distributed by Dominion Sound
Equipments, Ltd., and in the United States by authorized Independent Theatre
CENTURY PROJECTOR CORPORATION,
in 70mm reading:
The Cinerama page
Fred Waller's 1950 Diary
The Waller Flexible Gunnery Trainer,
By Fred Waller
A description is given of the equipment devised to train gunners
to hit fast-moving targets. The more important and novel features are
discussed. The trainer not only reproduces for the observer any desired
environment and target, but also correctly simulates conditions of fire in a
way that otherwise could only be found in actual combat.
1. Bird's-eye view of Waller Flexible Gunnery Trainer-Mark 2, showing
unified assembly of elements.
image to see enlargement
A humorous slant or gag often conveys an idea better than a serious
description. James Reddig, one of the Eastman engineers, was asked by
another friend of mine how the gunnery trainer had changed from the
experimental model he had seen and what it looked like. Jim replied, “Oh,
that's easy. You take the end off the Triborough Bridge, put four men on it
with their feet dangling in the air, a console like a church organ, and
behind that photocells, amplifiers, levers, scanners, and a lot of other
things that I cannot understand. Then, take the Perisphere from the World's
Fair, cut it into 4 pieces, push the end of the Triborough Bridge into one
of the pieces and you have a Waller Gunnery Trainer. It's just as simple as
As this description and Fig. 1 give you an idea of the size and complexity
of the machine, it is obvious that a complete analysis and description of
the apparatus cannot be given in one paper, so the following covers the more
important and novel features.
The purpose of developing this machine was to train gunners, under realistic
conditions, to estimate quickly and accurately the range of a target, to
track it, and to estimate the correct point of aim when using noncomputing
sights. To accomplish this purpose, the Waller Flexible Gunnery Trainer uses
a special spherical screen process. This process was conceived by Ralph
Walker, a well-known architect, and myself in 1938, and several years were
spent in developing the apparatus and overcoming the problems involved.
In June, 1940, H. Martyn Baker, an old friend of mine who is a graduate of
the Naval Academy at Annapolis, recognized the possibilities offered by the
spherical screen process in the training of gunners to hit fast-moving
targets. That was the real start of work on the gunnery trainer.
2. Perspective view of spherical screen upon which scene is projected.
The fundamental theory of the spherical screen process in that for the
average individual the perception of distance, beyond about 20 ft, is not so
much the result of binocular stereopsis as it is of peripheral vision,
relative movement, size of object and atmospheric perspective. By peripheral
vision I mean what the eye sees outside of its central area of sharp focus.
This screen process simulates what the eye normally perceives by filling a
screen, shown in Fig. 2, which is a portion of the inside of a sphere, with
a motion picture. The angular dimensions of the screen, 150 deg in the
horizontal and 75 deg in the vertical, are nearly those encompassed by the
normal human eye, and the angular relationships of any object, fixed or
moving, on the screen are the same as those seen by the eye in actuality.
Thus, the requirements of peripheral vision and movement perspective are
In the photography, the size and atmospheric perspectives are reproduced.
Therefore, the observer finds himself surrounded by a normal visual effect.
The success of the curved screen process in accomplishing this is evident to
anyone who has ever seen it.
3. Front view of trainer showing method of mounting and grouping of guns and
turrets around the projection unit.
image to see enlargement
For gunnery training purposes, a picture of the desired target, say an
airplane, is produced. To the observer this target does not remain more or
less fixed upon a single square screen covering only a small angle but moves
within his field of vision in an entirely normal manner thus enabling him to
exercise his judgment of distance and motion as though he were in the field.
. The observer is placed behind a dummy gun, located near the optical center of the screen, with which he attempts to hit the target.
By means of suitable apparatus described later, when the trigger of the gun
is pulled, and the gun is aimed so that a hit would be made, this fact is
instantly announced audibly in the gunner's earphones. This enables the
person being trained to make an immediate mental note of the judgment and
actions which led to success. In this way the Waller Flexible Gunnery
Trainer not only reproduces for the observer any desired environment and
target, but also correctly simulates conditions of firing in a way that
otherwise could only be found in actual combat. Since anything can be
produced on the screen that can be photographed, and since operation of the
trainer is independent of weather, time, and the availability of actual
equipment, it offers a valuable means of training in preparation for and
supplementing actual firing.
In order to cover a screen of 150 deg in width by 75 deg in height with
motion picture projection, it was found necessary to have 5 projectors to
obtain sufficient light on the screen. This dictated the number of cameras
needed to take the pictures.
The camera consists of five 35mm motion picture cameras synchronously
driven and operating as a single unit. This unit has been kept sufficiently
small and light so that it can be mounted in the gun or turret positions
available on bombers, or be used on a tripod ashore or afloat. The cameras
are arranged to cover, to the best advantage, a spherical angle of 150 deg
by 75 deg, and each one covers approximately a fifth of this total image. By
operating the camera unit in a gunner's position, it photographs what he
would see from this same position. In the trainer, these pictures are
projected on a spherical screen of the same total angles by means of 5
projectors which are arranged in the same relative positions as the cameras.
They reproduce the picture as photographed, that is, as if the gunner had
been in the same position which the camera occupied.
The screen is shown as a section of a hollow sphere of 20-ft radius. The
supporting framework is made of plywood, I-beams and intercostals. The frame
is covered with preformed plywood panels that are screwed in place. The
projection surface of the screen is given a special semispecular finish
which reflects light principally to the center, where the gunners are
placed. By doing this, it minimizes the degradation of the projected images
by cross reflection from one part of the screen to another.
Arrangement of Dummy Guns
Placed at even distances around the center line
of the projectors and the center of the screen are 4 dummy guns shown in
Fig. 3. Each gun is mounted on a heavy tubular mount and is free to train
and elevate so as to cover the screen. On the outside of the mount is a
bearing for a seat which slides on 2 tubes so that it may be adjusted for
men of different heights. The seat swings on a horizontal axis and is
supported by heavy spiral springs which are also adjustable for varying
weights of men. The seating arrangement gives full flexibility so that a
gunner can keep his eye in line with the sight.
Each gun is provided with a pair of handles, the right one containing a
trigger. When the trigger is pulled, the handles are vibrated by a pair of
motors in the dummy gun, simulating the recoil of a 50-caliber gun.
4. Sighting the target through the Mark 9 gun sight.
The instructor can disconnect the vibrator circuit if he so desires. On each
gun in the original model is mounted a Mark 9 collimator sight. Fig. 4 shows
what the gunner sees when he looks through his sight at the target in the
Subsequently, the trainer has been adapted to train men for sighting with
Sperry and Martin waist turrets, Sperry ball turrets, G. E. fire control
stations, as well as several different mountings for 50-caliber and 20-mm
guns, with and without lead-computing sights, and the Navy Mark 51
Director. Various combinations of these device were installed on individual
trainers as required. For training crews for the B-29's, 3 pedestal-type G.
E. Directors and one ring-type director are used.
Firing at Target
5. Schematic drawing showing flexible steel cable system from gun to
image to see enlargement
As the gunner looks through the sight and follows the target the resulting
movement of the gun, in train and in elevation, is transmitted, as shown in
Fig. 5, by a pair of light flexible steel cables running over ball-bearing rollers to train and elevate lever arms
in the unit called the "register". Each
pair of cables is kept under constant balanced spring tension so that
stretch or expansion and contraction from temperature changes have no effect
on its accuracy.
The lever for train and the lever for elevation each connect with opaque
masks having a transparent pattern of 2 fine lines. These marks slide
horizontally across the face of an aim scoring film in the register unit
associated with each gun. Figs. 6, 7, and 8 show details of linkage and
scanner bars and masks.
Scoring Mechanism in Register
6. Close up of sector arm to scanner bar assembly.
image to see enlargement
The function of the register unit is to determine whether the gun is aimed
at any instant to hit the target plane. It is this unit which receives the
existing train and elevation from the gun, and if the aim is correct, it
provides the means of sending electrical impulses to the instructor's
console where the hit recording counter for each gun is located.
The register is similar to one of the screen projectors and the film used in
the register operates in step with the screen picture films at a speed of 24
pictures per sec. The film used in the register is not a picture film, as
may be seen from Fig. 8. but is a hit scoring film specially prepared as
described under the scoring machine. There is a frame of register film to
correspond to each frame of picture film.
The register film is opaque and on each frame of the film are small
transparent areas. The areas are so spaced that they represent the position
at which the gun should be aimed to hit the target in the position shown by
the corresponding picture frame. When the gun is pointed at the correct
point of aim, transparent areas of the masks which the levers move will then
register with the transparent areas in the film. This allows the light in
the register projector to be transmitted to a photocell which, through an
amplifier and relay, actuates the hit counter mounted in the instructor's
7. Close-up view of scanner bar and gate assembly.
Each time the gunner pulls the trigger one burst for his gun is recorded on
the corresponding burst counter on the instructor's console. At the same
time, the bullet counter for his gun will record the number of bullets that
would be fired during the length of time in which he holds the trigger down.
If the gunner has his gun pointed at the correct point of aim when he pulls
the trigger, he will hear a high pitched tone in his earphones
instantaneously and he will score as many hits as the number of bullets
fired while he maintained the correct point of aim. If the gunner is not on
the correct point of aim when he pulls the trigger, he will still score the
burst and the bullets
fired but no hits. On trainers adapted for devices where range and aim are
fed in separately, 5 counters are used. The fourth records the number of
bullets fired while the gunner is putting in the correct range, and the
fifth the number of bullets fired while he is aiming correctly. On these
trainers the hit counter scores only when both range and aim are scored
8. Schematic drawing showing register film in relation to scanner bars and
method of registering film for scoring.
image to see enlargement
In order that the scoring on this machine may represent actual combat
conditions, the scoring film in the register unit may have different-size
transparent areas to allow for different-size vulnerable areas and targets,
or to allow for the area of the cone of gun dispersion. These areas may be
placed on the scoring film at different distances apart. If they are on
every other frame, they will record hits at the rate of 720 per min; if on
every fourth frame; at 360 per min, etc. By using this method, the gunner
will not only score hits in proportion to his accuracy of aim but he will
also score hits in the proportion which the vulnerable area of the target is
to the area of the cone of fire at the distance of the target.
That is, if the target at 600 yards has a vulnerable area of 30 sq ft, and
the area of the cone of fire is 300 sq ft, only one-tenth of the number of
bullets fired would hit the target. Both of these factors are taken into
consideration and the scoring gives a real indication of the man's ability
as a gunner. Some branches of the Armed Services desired to omit these
features and for them a constant angular tolerance of aim was used and all
hits recorded. By using film for the production of the register bands, great
flexibility is obtained.
9. Close-up view of the control panel on the instructor's console.
The instructor's console is mounted to the upper forward portion of the
structural framework, above the 5 projectors. From his position at the
console, shown in Fig. 9, the instructor may view the entire screen and the
2 upper gun positions.
The console has the following general controls and
(a) A running time meter to indicate total hours the trainer has been run.
(b) Switch to illuminate counters when house lights are off.
(c) A "still" button which allows instructor to hold pictures on screen for
5 min so that he may point out errors students are making in their aim.
(d) A "start" button.
(e) A "stop" button.
(f) Switch to permit talking to all 4 students at once.
(g) Projection room signal light to indicate "ready."
(h) Switch to communicate with office or projection room.
(i) Microphone head to contact students or projection room.
(j) Intercommunicating telephone with projection room.
In addition, 3 counters and the following controls are provided for each
of the 4 gun positions:
(a) Total number of rounds fired.
(b) Number of bursts filed.
(c) Number of hits obtained.
(d) Pilot light which flashes as each hit is scored.
(e) Microphone switch so instructor can talk to individual gunner.
(f) Vibrator switch by which vibrators on individual guns may be
(g) Aim projector switch which shows a one-inch diameter ring of light at
place on screen at which the gun is aimed. The student does not see this
light, since the central spot in his own sight covers it up but it allows
the instructor to see where that student is aiming. The ring is projected on
the screen by small projector mounted on the gun.
(h) Control knob, to return counters to zero.
(i) Pilot lights to indicate switches "on” or "off."
The Scoring Machine
10. Schematic plan showing method of projecting mosaics on the screen.
image to see enlargement
For the preparation of the aim scoring films which are used in the
registers, we have developed a special machine called the scoring machine.
This machine consists of the following parts:
(a) Five projectors for projecting the films one frame at a time.
(b) A 10 ft radius screen laid off in degrees of train and elevation on
which these pictures are projected and analyzed.
(c) Four pointers in the same relative positions occupied by the guns on the
(d) Four cameras connected to these pointers for making the original
negatives from which the scoring films are printed.
On this scoring machine,
the pictures are analyzed and a plot is made showing the range for each
frame of film, that is, each 1/24 sec.
Simultaneously, a record is made of the angle of the target, in both train
and elevation, in relation to the gun-carrying plane. A record is kept by
the cameraman, who makes the original negative, of the air speed and
altitude of the gun-carrying plane. With all this information, the Aberdeen
Tables give us the time of flight of the bullet. Knowing how many
twenty-fourths of a second it will take the bullet
to reach the target, we then aim the 4 pointers, which represent the 4 gun
positions, at the picture which is that many twenty-fourths of a second, or
frames of film, later. This gives the correct angular lead. By then
displacing each pointer the number of gunnery mils in both train and
elevation which the tables give as the ballistic corrections, we have the
correct point of aim.
By a system of cables and levers similar to those
connecting the gun and its register, each pointer is connected to a scoring
This camera makes a master negative scoring band for its gun. When the
scoring band is run in synchronism with the picture print from which it has
been made, it will record, to within a few gunnery mils, the correct point
of aim for the moving target shown on the picture film.
The projector unit is a group of 5 Century projectors operating in
synchronism as a single mechanism. All are of the same mechanical design and
each projects a portion of the whole picture upon the screen.
The optical axis of each projector passes through a common point, the focal
point of the screen, and radiates to 5 different areas on the screen, as
illustrated in Fig. 10.
The projectors are designed for use with 35mm
motion picture film, operating at 24 frames per sec. The running time of a
3000 ft reel is approximately 33 min.
A heat shield, which is a circular heat-absorbing Aklo glass filter and
associated mechanisms is located close to the rear wall of the projector.
It is mounted on a counterbalanced pivoted arm and operated by a solenoid in
conjunction with a limit switch which is related to a sequential circuit.
The purpose of the heat shield is to absorb and reduce the heat at the
aperture in the film trap and protect the film when still pictures are being
projected. Incidentally, during this period the radiant heat from the lamp
is also automatically reduced by dimming to a degree but still providing
sufficient light for still picture projection.
When the solenoid operating the heat shield is energized, it pulls the heat
shield into its place just back of the condensing lens assembly, where it
absorbs a portion of the radiant heat from the lamp before it reaches the
A cylindrical lamp house is mounted on the rear of the shutter guard. A
large hinged door extending half way around the housing permits access to
the interior for lamp replacements and optical adjustments. It accommodates
a 2100w incandescent filament lamp as the light source for the projector.
An inner tube, which surrounds the lamp, is part of the cooling system. It
serves to direct an air stream all around the lamp house to carry away the
heat generated by the lamp.
The system of forced air circulation in the
lamp house has been devised to remove normal generated heat that would
endanger the film in the projector and to provide cool operating conditions.
It includes the assembly of distribution ducts and air tubes associated with
the projector. They in turn are connected to an air supply and exhaust
system provided in the building.
The air is forced in at the top of the lamp house, streams past the full
length of the lamp all around the bulb as directed by the air tube within
the house, and the heat is carried off through the exhaust at the bottom of
the house to be dissipated at a distant point.
An additional cooling system is provided for the film. It is devised to
force a high-velocity sheet of air downward on both sides and over the
entire surface of the film in the film trap. The air is distributed through
a forked inlet pipe connection on the driving side of the projector and
passes through the center wall to the film or operating side. One tube leads
to the nozzle on the film trap, the other to nozzle on the film gate. After
the cooling curtains of air flow past the film surfaces they circulate about
in the immediate vicinity of the mechanisms in the projector.
Each projector is driven by its own electric motor, but all
motors are mechanically coupled together and held in synchronism by an
arrangement of beveled gears on a common synchronizing shaft that keeps all
projectors running at a speed of 24 frames of film per sec.
An additional motor called the framing motor mechanically
connected with the synchronizing shaft, serves to bring the projector
mechanisms to a stop with the film in frame and shutters open so that the
still picture projected is properly composed on the screen.
The photoelectric controls of the trainer
designed by W. Robert Dresser, are most elaborate and although not covered
here could easily be the subject of an entire paper.
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