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Fire Control |
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| As it
happens, fire control has been the most difficult section to put together.
Aside from scanning old photographs and blowing them up, there are not
many ways to obtain pictures or diagrams of these old fire control systems
(commonly referred to as "directors"). Few Museum ship curators
bother with these instruments because most tourists are not interested in
fire control directors. Tourists want to see the guns...BIG guns. The more
the better. Consequently, the guns receive priority for the few funds and
contributions museums receive. In addition, the directors are located on
the higher, more inaccessible locations of ships, a climb most people are
not willing to make. This was done as a practical matter--a higher
position provides better visibility, and a high position remains clear of
the smoke produced by rapidly firing guns. Basically there are four parts to a gunfire control system: the director, a "stable element", a ballistic computer and the guns. The director is the eye of the system and is usually located high on the ship to avoid the blast of firing and the resulting smoke. The director determines the direction and range to the target with either an optical rangefinder, telescope, or radar rangefinder. The "stable element", located in the bowels of the ship, was a collection of gyroscopes that measured the roll and pitch of the ship. The ballistic computer received the direction, range, pitch and roll information, added ballistic compensations, and adjusted the gun appropriately. Two ships I visited have retained their directors. The battleship USS Texas (BB-35), located in La Porte, Texas retained the Mk 52 directors but the access ladders have been removed, rendering them inaccessible to the public. I was able to climb hand-over-hand along an overhead cable to the port director. Once there, I was able to climb over the rear tower to access the starboard MK 52. Unfortunately, both directors are badly deteriorated and the photographs are useless. The second ship was the destroyer USS Kidd (DD-661) located on the Mississippi river in Baton Rouge, LA. This ship is in mint condition and has a wide selection of directors from different periods for different weapons. Most of the pictures below are from the Kidd and, as you can see, the curator & crew are doing a super job of maintaining this ship. If your wife will only let you visit one ship, this is the one! I spent a total of three days poring over this ship. Director basics: Hitting targets consistently requires several pieces of information. Most critical are direction and range. With these, you can point at the target and elevate the barrel to lob the shell at it. If the target is moving, hitting it becomes more complex because you have to lead the target enough so the projectiles arrive at a position the same moment the target does. This is known as "lead angle". Naturally, the faster the target moves, the more "lead angle" you need. (To try this at home, have one of your grandchildren stand still and throw a large rock at them. Easy, huh? Now have a different, uninjured grandchild run across the yard and try to hit them with a rock. Harder, huh? Keep trying until you score a solid hit...) Once direction, range and lead angle were solved, there remained the stability variable. Ships are not stable bullet-launching platforms. Even with perfect direction, range and lead angle, a bucking ship could cause a miss. (Again, have a third grandchild stand at the curb while you drive your car across a neighbor's yard and fling a rock at them. Really hard! HINT: borrow one of your kid's car for this. No sense in ruining your own.) Eventually, the navy solved this with a "stable element" which was nothing more than gyroscopes that were unaffected by bucking ships. Finally, as gun ranges increased, which meant more flight time for the projectiles, the earth's rotation, temperature, atmospheric pressure, humidity, and many other boring variables had to be accounted for. We'll ignore these & move on to directors on DEs. A directors was a centralized apparatus that provided elevation (estimated) and direction aiming information (the navy called it "pointing" and "training") to one or more guns. Later models provided lead angle and accurate range information. It was usually a pedestal-mounted reticle with a pair of bicycle-like handlebars for easy movement. One or more guns were "slaved" to a director. The first directors on Destroyer Escorts were the Mk 44s on the 1.1"/75 machine cannon. They were "dumb" aiming devices with reticle sights and were connected to the "slaved" gun. The director fed targeting information to each gun station, which displayed on a graduated dial. The gunner simply manually turned his control until the pointer on the gun matched the pointer on the graduated dial (called "matching pointers"). Once aligned, the gunner fired. Later directors improved on this by automating the guns with electric motors, improving on lead angle calculations, incorporating range-finding radars, introducing the "stable element", and including ballistic computers. 
The sequence of fire controls are confusing because
they had two designations, a standard "Mk" core and a two letter
designation. Since the designations are used interchangeably a quick
paragraph may save a lot of frustration. For main battery fire direction, the sets started with the Mk 3 (FC), followed by the Mk 4 (FD), Mk 5 (FE), Mk 6 (FF), Mk 7 (FG) and Mk 8 (FH), Mk 9 (FI), Mk 10 (FJ), Mk 11 (FK), Mk 12 (FL), and Mk 13 (FM). Most of these look alike but the most common are the Mk 4 and the Mk 12. For anti-aircraft fire direction, the Mk 4 (FD) was widely used but was soon replaced by the similar-looking Mk 12 (FL). Since the Mk 12 wasn't a good at detecting low-level targets, the Mk 22 ("orange peel antenna") was added for this purpose. Below are the directors used on Destroyer Escorts over their lifetimes. The Mk 37 director was used only with the 5-Inch/38 caliber, which was one of the standard conversions for DEs. The Torpedo director was, as far as I can determine after looking at hundreds of magnified photographs, never used on DEs. One torpedo man I interviewed insists they were on DEs, so I am including it. |
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| The Mk 44 Director was the Navy's first director of automatic anti-aircraft weapons. It was a simple "dummy gun" type director which was manually trained and elevated. It was used on the 1.1" AA machine cannon, which originally used only a ring sight and tracers to control fire. The Mk 44 contained optics and a spotting glass but had no lead angle computing elements. The common name for this director was the Mk 1 "eyeball." |
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The Mark 51 Gun Fire
Control System (GFCS) was the original equipment for the 40mm Bofors and 3"/50 main guns. The Mk 14 gun
sight, originally designed for the 20mm,
was a primary element of the Mk 51. The Mark 14 was the first
lead-angle-computing mechanism developed by the U.S. Navy and adaptation
of the Mk 14 to the Mk 51 GFCS began immediately after testing at Dahlgren
proving grounds in July 1941.
The first fleet installation of the Mark 51 GFCS
was in June 1942. The Mk 51 was a "dummy
gun" type director that was trained and elevated by a pair of
handlebars, similar to the 20mm gun. A range estimate was manually
adjusted on the side of the director and the lead angles computed by the
Mk 14 gun sight were transmitted to the power drives of the slaved guns.
Close-up of the Mark 14 gun sight. The Mk 14 was developed for the 20mm gun, but was also incorporated into the Mk 51 director. The Mk 14 contained two rate-of-turn gyros (one for train, and one for elevation), and a simple computer moved the sight relative to the gun so the gun led the target correctly. It had a fixed range of 5000 yards. It was also a nightmare to keep moisture out of. If desiccant bags weren't rotated regularly, the optics would fog up, rendering the sight useless. It could be furnished with the ballistics information for the 20mm, 40mm, 3"/50 and 5"/38 guns. The basic specifications were:
In May 1943, Dr. Charles S. Draper at MIT began working on an improved sight, the Mark 15. Similar in operation to the Mark 14, the Mark 15 had a 5.78 power telescopic sight with a field of vision of 8.9 degrees, which improved tracking. It was used to replace the Mark 14 throughout the fleet. The specifications were:
Wasting no time, Dr. Draper later produced the Mark 29 sight, the primary difference being the ability to cage the gyro. The Mark 29 was used only with the Mark 63 GFCS (which you can see below). The specifications were identical to the Mark 15. The entire Mark 51 GFCS was mounted on a pedestal and had a pair of bicycle-like handlebars extending to the rear. On the left handlebar was a trigger that, when depressed, "caged" or locked the gyroscope in place. When selecting your target, you "caged" the gyro until you were tracking smoothly, then you released the trigger to "uncage" the gyro so it could detect the rate of turn, thus calculate the proper lead angle. The right handgrip had the gun trigger. Once tracking your target, you could fire all slaved weapons (20mm, 40mm or 3") by pressing this trigger. Provided the gun crews had their triggers depressed, the weapon would fire on your command. If the pointer, trainer and gun captain did not all have their triggers depressed (they detected an unsafe situation, for example) the weapon would not fire. Once firing, you had to watch the tracers to see where the projectiles were going. This was because the Mark 14 had a fixed range of 5,000 yards. If the target was closer than 5,000 yards, the tendency was to lead too much. Targets more than 5,000 yards were led too little. The only way to adjust fire with the Mark 51 GFCS was to manually lead the target more or less. It was harder to adjust fire on the 3" guns because they did not have tracers. |
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| The Mark 52 GFCS worked in a
similar fashion except it had a ranging radar dish mounted on the front of
the mount that fed the proper range to a Mark 17 ballistic computer. The
ballistic computer calculated the proper lead angle, removing the human
range estimation from the loop.
These photographs clearly show the new position for the Mk 52 on the bridge where it replaced the 3.5 meter optical rangefinder. The rangefinder was moved lower onto the flying bridge as a backup rangefinder.
This is a rare shot of the flying bridge taken from the mast above. It clearly shows the Robinson's repositioned 3.5 meter optical rangefinder and the new Mark 52 GFCS. Courtesy of Adam & Mae Vanyo. |
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| The Mark 57 GFCS was similar
in appearance to the Mark 51 and Mark 52, but it had a Mark 28 Radar
(which had a 45" antenna) or Mark 34 radar (with a Mark 19
antenna measuring 30" diameter), a Mark 21 Radar Scope (see below) and
a Mark 17 computer. This system added a radar operator to the crew. The
gunner could track targets either optically or with the radar scope. The
Mark 57 added the "blind fire" capability to the guns and was
functionally equivalent to the Mark 63 GFCS below. The Mark 57 and
Mark 63 were developed simultaneously by competitors; Dr. Merle A. Tuve at
the Applied Physics laboratory and Dr. Charles Charles Draper of MIT.
Consequently, there was a great deal of similarity in appearance and
performance.
The CKB-55AJN-4, Radar Indicator, Mark 21, Mod. 4 was manufactured by the Hoffman Laboratories, Incorporated in Los Angeles, CA. It is a component of radar equipment Mark 25, Mod 1.
Quad 40mm Bofors with the Mk 34 Target Acquisition Radar with the Mark 19 antenna.
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| Right Side
view of the Mk 63 Fire Director. The Mk 63 used a Mk 19 X-Band ranging
radar (see above). The Mk 63
fire control system also included a Mk 28 ballistic computer and the Mark
29 stabilized gun sight. The Mark 63 GFCS provided the fleet with the
first blind firing capability for the heavy guns. Also developed by Dr.
Draper of MIT, the Mark 63 GFCS mounted the Mark 34 Target
Acquisition Radar on the gun system instead of
the director (see the Mk 19 antenna mounted on a 40mm above). The
first fleet installation of the Mark 63 GFCS was in November 1944.
Mk 29 Sight Right side view.
Mk 29 sight Left side view.
Mk 29 Front view.
Mk 29 Rear (gunner's) view.
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| Mark 27 Torpedo Director, panel view. The Mark 27 solved torpedo guidance problems by using information from the surface search radar, fire control radars, and the optical systems in the Mark 37 GFCS. Using that information, the mark 27 was able to calculate the target bearing, compute the lead angle, transmit the information to the torpedo launcher, and remotely fire the torpedoes. |
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| The Mk 4 (FD) director with the
Mk
12 ranging radar. Notice the similarities between the Mk 4 and the
Mk 37 below.
War Status: Used on Mark 37 and Mark 33 directors,
installed September 1941. |
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The Mk 37 Fire Director
was used on the 5"/38 Caliber gun and was
normally included as part of the upgrade package. The Mk 37 included the
Mk 12 ranging radar (the large dish). The Mark 37 GFCS was essentially an improvement of the Mark 33 GFCS that was developed in the 1930s. The Mark 37 relocated the ballistic computer, stable element and radar equipment below decks, leaving the range finder and tracking system in the director. Development began in 1936 with operational testing in 1939 and general fielding in 1940. At the time of fielding the Mark 37 was the finest fire control system in the world. It incorporated the finest optics, best radar, an excellent stabilization system, state of the art computation and data transmission, and remote control. It had a range of 18,000 yards and could handle a lead angle of 30 degrees. During world war II it was equipped with the Mark 1 computer and could engage targets traveling up to 440 knots. Following WW2, it was upgraded to the Mark 1A computer that could engage targets up to 880 knots. A complete system consisted of:
SPECIFICATIONS A later addition
to the Mk 37 Fire Director was the Mk 22 "orange
peel" radar mounted on the right side. The Mk 22 ranging radar was designed to overcome the
Mk 12's inability to reliably track
targets at low deflection angles. |
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The Range Spot Transmitter, Mark 2, Mod. 0, weighs 42 pounds and was manufactured by International Business Machines, Endicott, NY in 1942.
The Spot Transmitter, Mark 1, Mod. 0, weighs 99 pounds and was manufactured by International Business Machines, Endicott, NY in 1942. Both spot transmitters were licensed by Ford Instrument Company, Inc.
The 15-Foot Stereoscopic Rangefinder (not shown), was manufactured in 1942 and weighed 425 pounds. The ends protrude from the sides of the Mk 37 Fire Direction Controller.
The Target Designation Transmitter, Mark 10, Mod. 3, was manufactured by Bristol & Martin, Incorporated in New York, NY. |
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