Fire Control

Fire control notes from the September 1944 issue of C.I.C. (Combat Information Center) published by the U.S. Office of the Chief of Naval Operations.

Fire control notes and comments

fire control notes and comments...

Excerpts from ship reports with comments by the Bureau of Ordnance.

ON THE RADAR MARK 12

There is no comparison between the Mark 12 and the Mark 4 equipment in the ability to pick up targets at long range. Destroyers of the MAHAN and BUCHANAN types have been picked up consistently and easily in the 25,000 to 30,000 yard range band, in complete darkness, on CIC designation. “The maximum range on a DD recorded to date is 30,000 yards. Larger targets have not been tracked to extreme ranges.

A series 60 sled with radar screen was tracked easily to 20,000 yards. Aircraft are easily tracked to 55,000 yards. A drone was picked up at 36,000 yards over land. Approaching aircraft of combat types are easily detected at 40,000 yards.

The improved performance of the Mark 12 radar over the Mark 4 radar is due to the difference in transmitted peak power, the Mark 12 power being four times that of the Mark 4. This factor alone should increase range performance on targets above the horizon by about 40 per cent. The higher frequency also improves antenna gain.

ON TARGET WITH SEARCH RADAR HELP

A considerable amount of drill at picking up planes from search radar designation has been carried out, with extremely encouraging results. The average time to get the director on a low-flying plane at a range of 10 miles is about 25 seconds. That time includes training the director at least 90 degrees.

During a very recent drone firing one director picked up the drone over land at 35,000 yards. The plane had immediately faded on the SK radar, but the Mark 12 got the target, and a good Baker run was eventually fired.

The Mark to true bearing indicator now installed in Mark 37 directors is very helpful in picking up targets from CIC designation.

The pip-matching indication, superimposed oil the long range sweep on the train and elevation scopes was particularly designed to improve target acquisition. This presentation gives the pointer and trainer a complete view of all targets in the radar beam, and enables them to start getting on target before the target pip is notched. When notched, a change to “spot” or “meter” indication for more accurate tracking can be made.

DIRECTORS ON SEARCH RADAR PHONE CIRCUITS

During the night of 21 February 1944, while under plane attack off Saipan, the forward Mark 34 director, equipped with a Mark 8 radar, was able to pick up and track low-flying planes at will. Contacts were made as far out as 14,000 yards, generally between 6,000-8,000 yards, tracked as close as 1,900 yards, and then as far out as 25,000 yards (opening). Naturally, getting “on” was the most difficult problem due to the delay in surface and air search ranges and bearings reaching the directors from the radars through CIC. This lag was greatly reduced by the directors cutting in on the search radar phone circuits.

The ease with which the director crew tracked these low-flying planes offers serious possibilities worth investigating, of using the generated ranges resulting from such tracking in assisting the 40mm and 20mm gun batteries in opening fire.

NURSING MACHINE GUN BATTERIES ON LOW-FLYING AIRCRAFT

Single low-flying planes of both twin and single engine type, can be tracked from 15,000 yards on into the ship. The relative bearing and range obtained from the main battery directors is used to get the machine gun battery “on” low-flying night torpedo planes. The Mark 8 radar in some measure fills the need for information on enemy planes when they close within 6,000 to 8,000 yards, data not obtainable from the SK.

In one instance fire was opened at 1,900 yards using this information when it is believed the target would not normally have been seen until the range closed to 1,000 yards.

 

“Mobile Mattress” Radar

From Japanese Electronics, OPNAV-16-VP101, Photographic Intelligence Report 1, Air Intelligence Group, Division of Naval Intelligence, Office of the Chief of Naval Operations, Navy Department, January 1945:

“Mobile Mattress” Radar

A later, and apparently more efficient, Radar type is the “Mobile Mattress” or “Mark I, Model 2”. The Radar operates at 200 mcs. and is identified by a small screen (14′ x 7′) mounted on a Japanese standard army trailer (type 94).

This Radar is being used more and more for land-based search, either alone or in conjunction with older types. It is frequently seen mounted in emplacements, suggestive of a permanent siting.

Below are reconstructed drawings made from photos of the Kwajalein set.

The shack, antennae, revolving mount and trailer may be separated for shipping purposes.

Japanese Mobile Mattress Radar and Trailer

Namur, Kwajalein, Marshall Islands

LOCATION    KWAJALEIN
TYPE   (MK. I, MODEL 2)   “MOBILE MATTRESS”
ANTENNA    14′ x 7′ x 1 2/3′
FREQUENCY    200 MCS
P.R.F.   800 – 1500 PULSE   3 1/2- 12
MAXIMUM RANGE    100 N. MI.

The Mobile Mattress captured at Namur, Kwajalein, was mounted atop the standard concrete power house. Although the set is badly damaged, it is still possible to establish the important recognition features.

Note the similarity in design between this and the Attu type screen. The Mobile screen is much smaller, however.

Several additional views of the “Mobile Mattress” or Mark I, Model 2 are shown for familiarization. This set is very probably the best Japanese Search Radar in general use at present. The frequency is 200 megacycles per second and the maximum range is 100 nautical miles.

Japanese Radar of WW2

 

German Radar of WWII

From Japanese Electronics, OPNAV-16-VP101, Photographic Intelligence Report 1, Air Intelligence Group, Division of Naval Intelligence, Office of the Chief of Naval Operations, Navy Department, January 1945:

German Radar Summary

Examples of German Radar are included here to cover the possibility that the Japanese may have access to German equipment and technicians.

The Germans employ several types of land based installations covering the functions of Air Search, Fire Control, and Coast Watching.

These types are quite well standardized and are much more efficient than those the Japanese are known to have.

There is now some photographic evidence of German Radar equipment in use by the Japanese. Also, it is knowrn that many other types of German electronics equipment are being used.

The following table represents the latest list of German Radar types with salient information concerning each.

GERMAN LAND BASED RADAR
NameSize of Screen*Top of Screen Above GroundFrequencyRange in Nautical MilesUse
LIMBER FREYA20’x 16′
IFF – 16¼ x 3½’
26¾’
30′ with IFF
116-146 MCS.75A.S.
POLE FREYA 20’x 16′
IFF – 16¼ x 3½’ or 20′ x 8′
32′, 35′ or 40′ with IFF116-146 MCS.100A.S.
GIRDER CHIMNEY19½’ x 97½115′120-130 MCS.110A.S.
CYLINDRICAL CHIMNEY60′ x 97½
IFF .22′ High
110½’120-130 MCS.160A.S.
GEMA COASTWATCHER20′ x 8′25′370-390 MCS.Depends on elevation (ASL) of siteC.W.
LARGE COASTWATCHER35′ x 34′40′70-90 MCS.60-75C.W.
SMALL HOARDING63¾’ x 44¾’50′  C.W.
LARGE HOARDING98′ x 36½’50′120-130 MCS.100-115C.W.
SMALL WURZBURG10′ Diameter12½’ in Vertical Position550-580 MCS.25F.C.
GIANT WURZBURG24′ Diameter27′ in Vertical Position470-580 MCS.40G.C.I., A.S. & C.W.
* – Width (Horizontal Dimension) Given First
A.S. – Air Search
F.C. – A/A Fire Control
C.W. – Coast Watching
G.C.I. – Ground Control Intercept

Drawings of all of the basic German Radar types are included on this page. Best known popular names are used for the designation of each type. It will be noted that these designs are quite well standardized for each particular use, and identification is easier because of this fact.

In most cases, this German equipment is superior to that now in use by the Japanese. A constant watch for German type designs of Radar in Japanese held territory is therefore in order.

German Radar of WW2

 

Small Wurzberg German Radar

Report on the German “Small Wurzburg” radar from U.S. Naval Intelligence report Japanese Electronics, March 1945:

The “Small Wurzburg” or “Bowlfire” was first designed in 1936, and is one of the most efficient Radars. It is primarily for A.A. fire control but has been used for A/C reporting, searchlight control, and as a standby for Ground Control of A/C. In general, it is a mobile Radar, mounted on a four-wheeled trailer with outriggers for levelling. Some sets are emplaced, however, and the wheels removed.

Search is by mechanical rotation of the apparatus for bearing and by elevation of the reflector bowl for height measurement.

The diameter of the paraboloid reflector is 10 feet, the top of which is but 12½ feet above the ground. A cupboard, housing the radar equipment, and an operators seat are attached to the rear and side of the reflector.

Small Wurzburg German Radar

There are several types of Small Wurzburgs; among them Types “A”, “C”, and “D” are most used and are quite similar. Type “D” is found with limber mounting and may be without wheels or even set in concrete.

For transport, the paraboloid can be split, by hinges, and turned down in two halves.

Type F.M.G. 41-T is a modification of the Small Wurzburg which incorporates a scoop-like form for cutting out ground echoes.

The practical range of the Small Wurzburg is not more than 25 nautical miles but it has a high degree of accuracy for Fire Control purposes.

SO-7M Radar

The following report on the WW2 SO-7M truck-mounted surface search radar was published in the September 1944 issue of C.I.C. (Combat Information Center) published by the U.S. Office of the Chief of Naval Operations.

What the SO-7M can do…

The SO-7M—a truck mounted surface search radar with PPI presentation—is being furnished to Marine Corps Units and Naval Surface Search units. A performance test of the set tinder typical conditions was conducted by the Pacific Fleet Radar Center.

WW2 SO-7M Truck-mounted Surface Search Radar

The SO is mobile.

The SO-7M was sited on the shoreline with its antenna 20 feet above sea level. A 100 degree sector to seaward, with no line-of-sight obstacles, provided adequate area for the test. No difficulty was experienced in putting the equipment into operation. The time required for two men to do this was only about 15 minutes. The set appeared to be in excellent materiel condition.

Continue reading SO-7M Radar

Tail Warning Radar

Summary of Tail Warning Radar AN/APS-13 from Radar Observers’ Bombardment Information File, July 1945.

Tail Warning Radar AN/APS-13

Radio Set AN/APS-13 is a lightweight radar set which gives an airplane pilot, or any other aircrew member who can see or hear it, a visible and audible warning that a hostile airplane is behind or approaching from the rear.

The usable range of this set is from 200 to 800 yards, and within an area extending up to 30° on both sides of the airplane and from 45° above it to 45° below it. The set doesn’t work above 50,000 feet or below 3100 feet. Ground reflections determine the lower limit.

Tail Warning Radar AN/APS-13

The main units include the antenna, transmitter-receiver, indicator light with brilliance control; warning bell, ON-OFF switch, and test switch. The set operates on 27.5 volts, which is the primary aircraft power supply.

Operation

1. Turn the power switch ON.

2. Wait at least three minutes for the tubes to warm up, then hold the test switch up. If the indicator lights and the warning bell rings, the equipment is operating properly. You can adjust the intensity of the indicator light with the rheostat.

3. You must set the GAIN CONTROL correctly. Adjust the screwdriver control on the front panel of the transmitter-receiver so that the receiver sensitivity is well below the level at which the tube noise can trigger the relay and give a false warning. If you reduce the sensitivity too far, however, it won’t detect aircraft within the required range. Have a competent radio technician check this before you start out on a combat mission.

Caution: The warning bell must be where the pilot can hear it clearly but where crew members cannot hear it; they might mistake it for the bailout signal.

 

Airborne Jammer Radar Set AN/APT-1

A description of Airborne Transmitting Equipment AN/APT-1 used to jam enemy radars in WWII from Graphic Survey of Radio and Radar Equipment Used by the Army Air Forces, Army Air Forces, Air Technical Service Command, Wright Field, Dayton, Ohio, February 1945:

Transmitting Equipment AN/APT-1 is an airborne transmitter used to jam enemy radars in the 95-210 mc. frequency range. This band includes most of the enemy early warning radars such as the German Freya, Hoardings and Wasserman and Japanese radars of equivalent type. The equipment employs the DINA (Direct Noise Amplification) type of transmission and may be used either as a spot jammer or as a barrage type jammer.

The carrier frequency is suppressed and all of the output power is concentrated in the side bands, affording more effective jamming coverage with less power. It will effectively screen an AN/APT-l equipped bomber to within two miles of a Freya radar.

B-17 Bomber Radar Jammer

Radar Transmitting Equipment AN/APT-1 (Installed in B-17) may be used for spot or barrage jamming of enemy radars in the frequency range from 95 to 210 mc. (i.e. German Freya or Japanese equivalent types.)

For barrage jamming the equipment is adjusted to the required frequency prior to take-off, after which only the power output need be controlled.

For spot jamming the set must be tuned in flight by means of the control unit. Employing R-F Amplifier AM-14/APT or AM-18/APT the output of the equipment can be increased effectively. Two sets of three antennas are available for complete frequency coverage. All are of the quarter-wave stub type. One set is designed for vertical mounting and the other set is designed for mounting at an angle of 45 degrees.

Power is obtained from an 80/115 volt, 400-2600 c.p.s., a.c. source and a 28 volt d.c. source.

Test equipment required for the maintenance and tuning of the equipment includes Test Set I-139-A, Amplifier Alignment Unit TS-92/AP, Radio Frequency Wattmeter TS-118/AP or TS-92/AP, Pickup Assembly TS-131/AP, Test Set I-56-K and Frequency Meter TS-174/AP.

Army Supply Program requirements as of 20 November 1944 were 4,895 for the calendar year 1944 and 3,086 for 1945.

POWER INPUT   325 WATTS
POWER OUTPUT   30-8 WATTS (All sideband)
FREQUENCY   95-210 MC.
TYPE OF SIGNAL   DIRECT NOISE

TUBE COMPLEMENT
NO.TYPENO.TYPE
25R4GY16X5GT
36AC71931A
26C42832*
16V6GT/X1829B*
*One 829B substituted for one 832 for increased power over 95-150 Mc.

Radar Jammer Antenna Stub

(i) Antenna Stubs AT-36/APT, AT-37/APT and AT-38/APT are similar except they are for vertical mounting. (ii) Control Unit C-58/APT-1. (iii) Radar Transmitter T-28/APT-1.

RADAR SET AN/APT-1TOTAL WEIGHT 70 LBS.
ComponentNomenclatureSizeWeight
Radar Transmitter T-28/APT-17 5/8″ x 10 1/8″ x 21 3/4″43 Lb.
Control Unit C-58/APT-13 1/2″ x 3 1/2″ x 2 1/2″1 1/2 Lb.
Mounting Base MT-171/U 2 1/4″ x 10 5/8″ x 22″3 1/4 Lb.
Mounting Base MT-114/APT-15″ x 5″ x 3/4″1 1/4 Lb.
Antenna Stub AT-36/APT or AT-41/APTLength 16 1/2″6 1/2 Lb.
Antenna Stub AT-37/APT or AT-42/APTLength 22 1/2″6 1/2 Lb.
Antenna StubAT-38/APT or AT-43/APTLength 29″6 1/2 Lb.
and includes plugs, adapters, and misc. cables.

 

Speaking of Antennas…

Detailed breakdown of the communication and radar antennas mounted on the USS Yorktown from the Feb. 1945 issue of C.I.C. (Combat Information Center) published by the U.S. Office of the Chief of Naval Operations.

Speaking of Antennas…

USS Yorktown, one of the Fleet’s mighty flattops, goes forth to track the Japs with this forest of radar antennas. Air and Surface search, GCI for night interceptions, fire control, beacons, interrogators, intercept receivers (not shown)—the array is complete, the ship ready to detect the enemy despite all his desperate efforts to evade, deceive, or jam.

USS Yorktown Aircraft Carrier Flattop Radar Antennas