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Ballistic Computer |
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best I can determine, this is the only remaining reference to the Mark 1
ballistic computer. Everything on this page is a result of conversations
with former-crewmembers. I have been unable to locate any written records,
manuals or references to the computer. Procedurally, I have no idea how
this works or how many crew members were required to operate it. I do know
it was used until at least August 1956, because that is when the last
modification (mod 13) was accomplished.
Here is the story of the Mark 1: It is 1930 or 1931. For years we have been lobbing shells at targets that are well beyond our range of sight. Unfortunately, shooting at targets we can't see is not efficient and results in a lot of wasted ammunition. Our guns, projectiles and propellant technologies are so advanced they can reach targets beyond the visible horizon, so improved optical systems will not help. Radio communication is relatively common so we could use a forward observer to "call our shots", but this depends on someone actually laying eyeballs on the target. If he can see the target, the target can see him. Not good. The Allies are perfecting radar and this seems the perfect solution for finding and ranging enemy targets, but range and direction are not enough information to hit our target. By the time we gather the variables we need to hit the target (range, direction, atmospheric pressure, atmospheric temperature, propellant temperature, gun tube temperature, projectile weight and temperature, flight time, corriolis effect, etc., our target is back in his home port. We need a fast way to factor in all variables for our firing solution so we look for help at the Washington Navy Yard. They gather hundreds of women at the Washington Navy Yard in Washington, D.C. and spend months hand-calculating every possible combination of the variables to build the first "firing table". This was no small task because the number of variables was extensive. I'm no artilleryman, but just combining the 10 simple variables above would lead to over a million calculations! Surely there were more variables than ten, so the resulting firing table must have been mountainous! They soon realized they needed a machine...a computer. Engineers started working. In the early 1930s Ford Instrument Company of Long Island City, New York introduced the Mark 1 ballistic computer (and charged the USN $75,000 per copy). The Mark 1 could solve ballistic problems in only the x (range) and y (direction) axes. About 1935 Ford Instrument Co. added the ability to the Mark 1 computer to solve rate changes in the z (elevation) axis. The Mark 1 could compute in fixed elevation, it just could not compute changes in terms of elevation, as are found in moving aircraft. Therefore, the Mark 1 was useful primarily for surface-to-surface use and could not solve for surface-to-air problems needed for an anti-aircraft role. The Mark 1A solved this by calculating for elevation changes and could calculate solutions for surface-to-air targets traveling up to 450 knots. The Mark 1A became the Navy’s first Dual-Purpose computer. The Mark 1A dual purpose computer together with the 5”/38 in single and twin mounts were deployed on almost every USN ship from destroyers through battleships and carriers by the end of WW II. As the Jet-age came about in the late 40’s, the computer was modified to allow maximum target speed about 650 knots. Around 1935 the Mark 1A "Ford Range Keeper", the machine below, was ready. It has three major components: The computer itself, the star shell computer, and a stable element. Each of these are documented and described below. The Mk 1A required at least 3 operators (speculation) as there appear to be three working locations requiring input of a variable. The variables are connected through internal gears and a change in one variable results in minor adjustments of all others. It worked. American ingenuity at work... |
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| Here is a scan from the operator's
manual showing details of the control panel. This will give you an idea of
the overall layout since my photos were taken in a restricted space. When
I complained to Jesse Eaves about being unable to frame the entire Mark 1
into a single photograph, he offered (with a completely straight face) to
move it topside for easier photographing.
Specifications
of the MARK I Computer: |
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| The Mark 1
Computer on board the USS Hornet (CV-12) on 21 June 1945. These four
photographs were classified SECRET
until the late 1970s.
The stable element (with the pistol grips sticking out) is on the right.
National Archives #80-G-367549 |
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| The following
three photographs reveal the incredible complexity of a mechanical
computer. The gears, solenoids, switches, pushrods and electrical wiring
are literally crammed into the casing. To accomplish any task the workman
would have to have very small hands and a high degree of manual dexterity.
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National Archives #80-G-382906 |
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| The Mark 1 Computer weighs 3,150
pounds and was manufactured by Hannibal C. Ford Instrument Company on
contract number 029828. This picture of the Mark 1 Computer taken from
outside the computer room. Note the sheer size of the case. It is
constructed of heavy cast aluminum with external strengthening ribs.
Heavy duty! The box closest to the door is the Mark 1 computer. The smaller
box on top with the black dial in the top left corner is the Star Shell
Computer, which is detailed below. The Stable element is behind the
computer and is also detailed below. The shell of the ship's master gyro
compass is visible on the bottom right. The gyro compass is detailed on
the website under the ship's equipment section.
On the top of the computer are several indicator dials and their associated control knobs. This is the output for the pointer's signal.
This is the output for the trainer's signal. (sorry about the glare. There was a lamp directly above the panel reflecting off the glass. This is the best of 5 photos.)
This was the input for the rangefinder's range in yards, either optical or radar and the height in feet.
Input for the target speed, projectile time of flight, rate of climb in knots, target rate of dive in knots, and the target horizontal speed in knots. Confused yet? |
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Mounted on top of the Mark 1 Computer is the Mark 1, Mod 0 Star Shell
Computer, weighing 215 pounds and manufactured by Ford Instrument
Company, Incorporated in Long Island City, New York in 1943.
The Mk 1 Star Shell Computer was designed to deliver illumination rounds to a precise height and location. Ideally, the illumination rounds would trigger 1000 yards beyond, 1500 feet above the target and float down on parachutes, running out of fuel at the precise instant they hit the water. The star shell section of the computer allows you to take one gun mount or turret and reposition it to fire star shells for target illumination for the other weapons. This section of the computer takes the generated or computed firing solution and allows the operator the control necessary to offset the gun from the target position. Offsets can be set into the star shell section to correct for range, bearing, elevation and the prevailing wind so as to correctly position the exploding star shell. |
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| The front panel of the Mark 1,
Mod. 0 Star Shell Computer. Details of the individual dials are
below.
The left indicating dial indicates the range (in thousands of yards) and time to set on the Star Shell Mechanical Time fuze (in seconds). The center digital dial indicates the star shell range (in yards) and the right indicator shows the range spot in hundreds of yards.
The target course indicator in degrees. This dial is not directly visible in the front panel view but the ring is partially visible at the top right of the case.
The main control panel for the Mk 1 Star Shell Computer.
The indicator on the right displays sight angle (in minutes), Sight deflection (in mils), fuze setting (in seconds), and the advance range (in yards). The fuze setting probably became obsolete with the introduction of variable time (VT) fuzes. The VT fuze contained a miniature radar it the glass nose that triggered the explosion when it sensed close proximity to the target, hence the name "proximity fuze."
Display of elevation synchronization.
Shot correction information to include range spot (in yards), elevation spot (in mils), and deflection spot (in mils). |
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| The Mark 6, Mod. 8 Stable Element contains a gyroscope that spun at 8,500 RPM and compensated for the ship's pitch and roll in ballistic computations. I had been looking for the mysterious "stable element" but, convinced the last one had been destroyed years ago, had given up on ever seeing one. In case you want further information, I am including the contract and drawing numbers whenever available. | |
| The front view of
the Stable Element. The glass-faced port hole on the front allows
you to look in and see the gyroscope. It weighs 873 pounds and was
manufactured by ARMA Corporation in Brooklyn, New York in 1943. It is
designed on Ordnance Drawing Number 228041 and purchased under Contract
Number 77900.
Rear view of the stable element. The Mark 6 Stable Element was the firing station for the plotting room and had controls to trigger the 5"/38 guns. In the adjacent picture you can see the copper pistol-gripped firing triggers for the slaved guns. Also, notice the center grip has knobs, making it easily recognized by touch in the dark or in smoke.
Top panel of the Stable Element displaying the cross-leveling information necessary to compensate for a bouncing ship
The Stable Element Control Panel, Mark 7, Mod. 5, weighs 315 pounds and was manufactured by ARMA Corporation in Brooklyn, NY on contract number ORD-6952. It is based on Ordnance Drawing Number 291115. |
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