“AT THE READY”
The presentation will be very brief and devoid of most of the details by the necessity of limited space.
The first order of business will be the director/radar system (very briefly) because it is the source of the original parameters to solve this geometric problem. The steps involved are: determine continuously the present target position in relation to own ship; predict future target position in relation to own ship (line-of-sight (LOS) displaced from line-of-fire (LOF) by time-of-flight (Tf) and correct- ions); stabilize the various units; calculate required corrections to gun train and elevation; and transmit data to the gun. So, the system must determine target range, bearing, course and speed, and make corrections for own ship course and speed, wind, drift, pitch and roll, heave, etc.
But first, the radar (and its LOS) , on top of the director, must be stabilized to counteract the effects of the ship’s pitch and roll (so as to obtain stabilized measurements). To do this, the pitch and roll are resolved into level and crosslevel so that the LOS remains in the vertical plane. This will be seen in the following diagrams on the next page. (Pages will be continuous in this way.)
COLD AND BLUSTERY
The writer, lower left, is standing on the After Bridge (BAT 2), a covered sighting telescope behind him and a signal lamp back of that. Above the signal lamp is the P.A. loudspeaker and to its left is a lookout with sound-powered headphones. And yes, it’s cold and blustery (and miserable) out there, especially for those Airdales who are unprotected on the flight deck going about their business.
The Mark 6 Stable Platform measures the level angle L and the crosslevel angle Zd used to maintain the radar antenna perpendicular to the horizontal plane (surface of the ocean), thus keeping its LOS in the vertical plane (a requirement for the geometries to follow). This is done by using the characteristic of a gyroscope, the rotor of an induction motor that spins at 140 rev/sec, to establish a true vertical and its associated true horizontal plane. A gyroscope has the properties of “gyroscopic inertia” and “precession”. Because of inertia, a spinning gyro tends to keep its axis pointed in a fixed direction at right angles to any force applied to it. The gyro’s spin axis is maintained in the vertical position automatically by two mercury tanks connected by a tube. As the gyro wheel goes out of the horizontal plane, one tank fills as the other loses mercury. The added weight of the filled tank will cause precession to return the gyro wheel to the horizontal by means of a “gimbal rotation motor”. The stable element receives own ship’s course Co and target bearing B’r from the computer to orient the gimbals to LOS. It transmits crosslevel Zd to physically stabilize the radar antenna to true vertical LOS2. Above, the electromagnet is the primary and the “umbrella” is the secondary of a transformer. When the ship’s deck is perfectly horizontal the electromagnet points directly at the intersection of the level and crosslevel coils, and the voltages induced in the coils by transformer action are equal and opposed so no current flows. If the ship is tilted, however, the gimbals move and the magnet then points at some other location on the umbrella thus creating unequal voltages. These level and crosslevel voltages are transmitted to the follow-up motors to reposition the gimbals to their undisturbed state. The crosslevel voltage represents the value sent to the radar antenna motor that in turn maintains the LOS2 (above) in the true vertical plane (the LOS is generated by the radar).GUNNERY PRACTICE
The spent shells on the deck have been ejected from the openings of the gun-mount. Also, just below the 40-mm guntub, on a pedestal, is its director (probably MK 51 with a MK 14 optical sight. The gunner simply tracks the target, letting the director generate the lead.Now that the Stable Element has physically righted the radar antenna in the true vertical plane, the director/radar generates the target’s slant range, elevation (Eb, elevation of the antenna LOS above the deck measured in the vertical plane through the LOS), and bearing (B’r, the angle between the vertical plane through the fore/aft axis of own ship (OSCL) and the vertical plane through the LOS measured in the deck plane clockwise from the bow of own ship) of the target from the ship. This is a tracking radar whose function is to follow a moving target wherever it goes.(as opposed to a search radar that keeps track of all ships and/or aircraft in the area). A Radar MK25 detects targets by sending out pulses of UHF radio waves from a high-powered transmitter. These pulses are concentrated into a narrow beam by means of a conical or parabolic antenna (such as a directional searchlight). When the transmitted energy (beam) strikes a metal object (aircraft), a portion of it is reflected back towards the transmitter (such as a sound-echo). This returned energy is detected by a radio receiver and then translated into a form of useable data on a radar console (similar to a computer console). Since radio waves travel at 186,000 miles/second, the elapsed time of the transmission and return of the reflected wave can be converted into the range that the target is from the ship. That the transmitted radar beam is narrow and directional, so too can the direction of the target be determined (by recording the direction of the director/radar antenna at the time of detection of the target). The radar system consists of the following: modulator (a timer that synchronizes the transmitted pulses with the indicating units); transmitter (generates short, powerful radio pulses); antenna system (radiates the pulses in a narrow, directional beam and receives any returned energy from the target); receiver (amplifies the weak returned signals from the target and reproduces them as video on the displays (indicators)); indicator ( cathode-ray tube (similar to a computer screen) to provide a visual indication of returned pulses that provide the required data for continuously tracking the target); power supply (supplies all the regulated dc and ac voltages required by the system). The range measurement is determined by applying the transmitted pulse to the indicator (CRT) along with the received pulse. There is a time-scale on the horizontal axis of the CRT that indicates the time for the pulse to go out and back. This in turn is applied to conversion circuitry to produce the range. For elevation and bearing, returned pulses are greater or lesser in magnitude in direct proportion to the target’s offset from the center of the narrow beam. The transmitting feed-horn at the center of the antenna is physically rotated about the LOS at a 5 degree angle, and at 10 cps (cycles/sec.). The radar’s modulator generates two 10 cps voltages separated by 90 electrical degrees (sine and cosine). The returned beam is modulated at 10 cps (a high value when directly on the target and and a low value when off the target). This return-beam is demodulated (the “sine wave” component is removed from the UHF component). Now this demodulated wave is compared with the generated sine and cosine waves. The greater their phase difference with the returned demodulated wave, the further the beam is from the target (sine=vertical, cosine=horizontal). These two differences are error signals which are used to drive a motor to bring the beam (and the radar/director) back into coincidence with the LOS. As the director moves, it moves the rotor of a synchro whose stator windings’ voltage represent the director/radar’s elevation and bearing.
“BOOOOOM !!”
When I was participating in gunnery practice, previously described, I was standing in front of the 40-mm gun-barrels to my left (pointing outward) with the 5-inch gun-barrels to my right, also pointing outward, almost within arm’s reach. Then, with nary a word of warning, the 5-incher lets go with a pulverizing “BOOOOOM !!”, as here. I still think that I made a world’s record vacating the site.
The fire control problem that must be solved includes continuously determining the present target position; performing ballistic correct- tions, whereby the axis of the gun bore is offset from the LOS; performing corrections for the gun platform motions of pitch and roll (and heave); making up gun orders; and providing corrections to inaccurate solutions of the analytic problem and for equipment inaccuracies. The target position is of interest at three specific times: (1) present target position, (2) target position at any given instant (generated target position), and (3) target position at the end of a specific time, that time being Tf (advance target position at point of impact with the projectile). The analytical solution starts with the determination of the target position with respect to own ship: (1) Present Range (R) along LOS from ship to target; (2) Relative Target Bearing (Br) from ship to target in horizontal plane; (3) Target Elevation (E) of target above ship along LOS. These values are continuously provided by the director/radar. The ship’s speed So is continuously provided by the ship’s pitometer. The values of the bearing angle A, the target’s horizontal speed Sh, and the target’s vertical rate of climb are all estimated by the FC Officer visual observation of the target. As is seen on the diagram to the left, the values for dRh and RdBs are obtained by simple geometry. These values will be used on the next page. But first, mention must be made as to how these, and other computations, are accomplished. There were no digital computers back then with all their speed and capacity. No, there weren’t even any electronic analog computers that preceded the digital technology. What was available was an ingenious device that made mathematical computations using mechanical instruments (a rangekeeper, the Mark 1A computer). These instruments were; (1) shafts whose rotation represented a number; (2) gears whose teeth generated ratios; (3) differentials that performed addition and subtraction; (4) cams that represented nonlinear functions; (5) component solvers that resolved vectors into right angle values; (6) integrators which multiplied a constantly changing value, such as time, by a variable such as range rate, the output being a continuous value of their product which can be accumulated as a shaft rotation; (7) multipliers which can take two continuously changing input values and deliver an output that is proportional at every instant to the product of the two changing inputs. This rangekeeper has tracking, prediction, and correction sections. There are many hand-cranks to manually, continuously input values. What a mechanism! GUNNERY PRACTICE
These are two open gun-mounts, back aft, port side, being pointed by an optical-sighted gyro-stabilized director. Notice the LSO’s (Landing Signal Officer) wind-screen, and safety net into which he dived should a landing aircraft come that close upon landing.
The director/radar can measure only changes in range along the LOS, changes in target elevation perpendicular to the LOS in the vertical plane containing the LOS, and changes in target bearing at right angles to the LOS in the horizontal plane (the letter “d” before a quantity means “time rate of change”, such as mph). This diagram shows how the linear rates of change in range dR and elevation dE are obtained (they are both in the vertical LOS plane). The components dR, RdBs, and RdE form the basis for the generated rates and predictions of future target position. Three steps are required if accurate values of gun train and gun elevation are to be continually and accurately computed: (1) checking and correlating the FC Officer’s estimates of target movement (angle A, Sh, dH of previous page); (2) maintaining a reliable figure at all times for the present value of target range, bearing, and elevation of the future position of the target. Having dR and dE, it remains to obtain dBr so as to compute the generated (computed) target position (cR, cBr, cE). The value dBs is measured in the LOS slant plane (“s”), but it is necessary to find the value in the horizontal plane (dBr). Thus, RdBs is divided by RcosE to obtain dBr. Now the generated target position is derived from cR = jR + #T(dR), cE = jE + #T(dE), and cBr = jBr + #T(dBr), where “#” means a change in that quantity during some specific time (i.e., it’s an increment of something) and the letter “j” means a correction to a quantity (the difference between generated and observed change in range, bearing, and elevation). Now predicted target position refers to the diagram on the next page. Based on the assumption that the present rates of relative motion dR, dE, and dBr will remain constant for very short periods of time, they can be used to predict the target’s position at the end of the time of flight (Tf) of the projectile. The results may be considered as determining an appropriate “line of fire” (LOF). Because of the high speed of the target, the LOS and the LOF may be far apart. (The time of flight Tf may be computed thus: Tf = Range/Rate = 27,000 ft./2600 ft./sec. =3.46 secs.) The future target position is indicated on the diagram on the next page and is defined as R2 = R + dR(Tf), E2 = E + RdE(Tf/R2), and bearing as Br2 = Br + RdBs(1/cosE)(Tf/R2). The next order of business is to determine the gun orders E’g and B’gr as modified by the ballistics of the projectile: gravity, drift, wind, loss of initial velocity (I.V.), and certain geometric errors introduced by the fact that the motion of the gun is limited to train in the deck plane while elevation is perpendicular to the deck. That is, the guns are affected by the ship’s pitch and roll as well as is the director/radar. Since the target is relatively close, these errors are less significant than with ship targets. FORWARD GUN-MOUNTS
These are the open gun-mounts, up forward on the port side. Notice how high the gunner must lift the projectile (55-lbs.) and the shell casing when the gun has such a low elevation. This is real work, especially when time is of the essence when an aircraft is boring in at you. Also notice the scuppers at the outside edge of the flight deck used to drain water away from whatever is below the deck.
The sum total of ballistic offsets from the LOS is called the sight angle (Vs) and sight deflection (Ds). Vs is the difference between elevation of the gun axis (LOF) above the horizontal plane (not the deck plane) and the elevation of the line-of-sight (LOS) above the horizontal plane (not the deck plane), measured in the vertical plane through the LOF. And Ds is the angle between the vertical plane through the LOS and the vertical plane through the LOF, measured in a plane perpendicular to the vertical plane through the LOS. (See the figure on the right, next page. Since this figure does not show the deck plane, E’g = Eb + Vs instead of the final value of E’g = Eb + Vs + Vz, where Eb = E + L and Vz accounts for the gun tilt due to the crosslevel Zd (pitch and roll). Similarly, B’gr = B’r + jDd + Dz, where Dz accounts for the same crosslevel Zd. Vs, Ds, Vz, Dz, and jDd will be explained later.) In the figure, this page, the predicted change of range dR(Tf) equals Rt. The predicted angular change of elevation RdE(Tf/R2) equals Vt, and the predicted angular change of relative bearing of target from ship RdBs(1/cosE)(Tf/R2) equals Dt. Thus, Vs = Vt + Vw + Vj + Vfm + Vf - Vu - Vx where Vt is the elevation prediction, Vw is the wind elevation correction, Vj is the visual elevation spot of the projectile explosion, Vfm is the initial velocity elevation correction, Vu is the air density correction, Vf is the superelevation correction (the higher the target, the more correction required), and Vx is the complementary error(due to the target’s linear motion while the gun-trunnion trains in an angular mode), Also, Ds = Dt + Dw + Dj - Dfs where Dt is the deflection prediction, Dw is the wind deflection correction, Dj is the visual deflection spot of the projectile explosion, and Dfs is the drift correction. Finally, the range Rs, which enters into the determination of the above enumerated ballistics factors, is Rs = cR + Rt + Rw + Rj + Rm + Rx + Re where cR is the generated present range, Rt is the predicted range, Rw is the range wind prediction, Rj is the visual range spot, Rm is the initial velocity range correction, Rx is the change in advance range due to the deflection (train) motion, and Re is the change in advance range due to elevation Vs. Unlike the figure on the next page, right, the deck is “never” horizontal. Also, the gun orders are based on the director’s LOS, and the lead angles Vs and Ds must be continuously corrected for the ship’s pitch and roll motions. Since the gun’s motion is limited to train in the deck plane and to elevation in the plane perpendicular to the deck, gun orders must be (cont.)POSED BUT REAL
Should the automatic director become inoperative, the gun must be directed manually by hand-cranks as shown here, one for train and one for elevation. A grim picture indeed, but then, this is indeed a grim business, especially if it is a kamikaze bearing in at you.
computed in those planes. These corrections are not included in Vs and Ds due to how fast they change, but are included in the gun orders. Accordingly, gun elevation order E’g contains (1) the elevation of the dir- tor LOS above the deck plane Eb = E + L, (2) the vertical offset Vs to account for prediction and ballistics, and (3) the trunnion tilt correction in elevation Vz, or E’g = Eb + Vs - Vz. The gun train order is made up of (1) director train B’r, (2) the lateral offset Ds to account for the prediction and ballistics, and (3) trunnion tilt correction Dz. Actually, Ds is in the slant plane and must be projected into the deck plane as jDd (“s” is slant, “d” is deck, and “j” is correction. Remember, the above, right, figure is in the horizontal plane.) Thus, the gun order for train is B’gr = B’r + jDd + Dz. The above description of the solution of the fire control problem, as has been said, makes use of the proximity fuse which accounts for those bomb-bursts that are seen in the final chapter of this book. So there it is, that veritable marvel of engineering prowess, the 5-inch gun system whose sole purpose was to protect the ship and those on it. The preceding pages did not even scratch the surface of describing the intricacies or the technical wonders of this system. What was said is fully accurate, I believe. But in truth, it only provided the “flavor” of the system. The engineering acumen exhibited in this system was a very direct progenitor of the sterling capabilities of our present day productive infrastructure, to which we all are in debt. It’s really too bad that so many take so much for granted. To paraphrase one of the wartime leaders, never have so many owed so much to so few (engineers). My entire career has been in this field (Navy Dept.) and I only wish I could have had more impact in it. I’m subdued. 