Navigation Sets


SCR-518-A or AYA High Altitude Pulse Altimeter

SCR-518-A in B-17
SCR-518-A in B-17
Radio Operator's Position
Radio Operator's Position

DESCRIPTION: Absolute pulse radar altimeters.
USES: For measuring absolute altitude in high-altitude bombing, photographic mapping, terrain clearance.
PERFORMANCE: SCR-518-A and AYA operate between 50 ft. and 20,000 ft. Accuracy is ± (50 ft. plus 1/4%).
TRANSPORTABILITY: SCR-518-A is packed for shipment in one unit, weighing about 150 lbs. and occupying 30 cu. ft. AYA is packed in 3 units, weighing 207 lbs. Largest unit measures 30" x 281/2" x 261/2".
INSTALLATION: Average installed weight of SCR-518-A and AYA is 100 lbs., effecting a drag of not over 10 lbs. at 250 mph. Indicator (a cathode ray tube) cannot be successfully mounted where pilot can use it.
PERSONNEL: Altimeter is operated by the radar operator or bombardier, and can be serviced by regular radar maintenance personnel.
POWER: Total primary power required is 11 amps., 27.7 v. DC for SCR-518-A and AYA.


*SCR-718 Pulse Altimeter


DESCRIPTION: Absolute pulse radar altimeter.
USES: For measuring absolute altitude in high-altitude bombing, photographic mapping, terrain clearance.
PERFORMANCE: SCR-718 operates between 50 ft. and 40,000 ft. Accuracy is ± 50 ft. plus 1/4%.
TRANSPORTABILITY: SCR-718 is crated in one unit weighing about 60 lbs., and occupying about 12 cu. ft.
INSTALLATION: SCR-718 weighs 40 lbs. installed and is mechanically and electrically interchangeable with AN/APN-1 except for indicator and AC power connection.
PERSONNEL: Altimeter is operated by pilot and can be serviced by regular radar maintenance personnel.
POWER: 135 watts, 115 volts, 400-2600 cycles AC.

* Available for issue in latter part of 1943.


AYB, AN/ARN-1 (RC-24 & AYD-5) & AN/APN-1 (AYF)
Low Altitude FM Altimeters


DESCRIPTION: Absolute FM radar altimeters.
USES: for use in sea search, torpedo launching, low-altitude bombings, as a photographic aid, or landing aid. Indication is provided on a meter.
PERFORMANCE: All sets operate between 5 and 400 feet, measuring altitude with an accuracy of ± (5' + 5%). AN/APN-1 also operates between 400 ft. and 4,000 ft., with an accuracy of ± (60 ft. + 5%).
TRANSPORTABILITY: Sets including spares for 200 hrs., packed for shipment in two units weighing about 60 lbs. Largest package measures 25" x 171/2" x 151/2".
INSTALLATION: Average installed weight is 35 lbs., producing a drag of not over 15 lbs. at 300 mph.
PERSONNEL: Altimeter is used by the pilot. Regular radar maintenance personnel can service the equipment.
POWER: Sets require primary power of about 75 watts 28 v. DC, from plane's DC supply.


SCR-640, SCR-621 or YH, & *YJ Long Wave Racons

Racon Installed on Hangar
Racon Installed on Hangar

DESCRIPTION: Long wave racons, transmitting a coded identification signal when triggered by radar in planes. YJ is fixed; SCR-640, SCR-621 and YH are fixed or mobile.
USES: For homing friendly aircraft to their bases, or as a general navigational aid. SCR-640 works with SCR-540 airborne set; YJ and SCR-621 or YH with SCR-521, ASVC and ASE airborne sets. YJ also works with ASB sets.
PERFORMANCE: YJ has a reliable maximum range of 80 mi. Other sets have a reliable range of 85 mi. Range accuracy is ± 5%. Azimuth limits: 360°.
TRANSPORTABILITY: YJ will be crated in 3 units for shipment. Total weight is 550 lbs. Largest unit is 72" x 24" x 24" and weighs 225 lbs. All other sets, without generator, are packed for shipment in 3 units, weighing a total of 660 lbs. The largest unit is 24" x 24" x 48" and weighs 300 lbs. (Antenna tripod measures 12" x 12" x 144"). With generator, sets are packaged in 5 units, weighing a total of 1000 lbs. Largest package is 44" x 33" x 26", and weighs 475 lbs. Shipments include spare tubes for 1,000 hrs.
INSTALLATION: Sets should be sited at any ground location accessible by motor vehicle (YH and YJ are also installed on ships.) The 20' antenna should be clear of surrounding objects for a radius of 100 yds. 3 maintenance men can install racon in 3 hours; if truck-mounted, racon can be put in operation by 1 man in 1 hour.
PERSONNEL: No operators are required, but maintenance men should make a 10-minute check every 4 to 8 hours. Consideration is being given to continuous monitoring in view of importance of navigational facilities provided.
POWER: Total primary power required is 150 watts (for YJ) and 419 watts (for other sets), 115-230 v., 50-70 cycles, AC. Gas engine driven generator, supplied on request, uses standard 70-80 octane gas at rate of 0.25 gal. per hour.
* Available for issue in latter part of 1943.


*AN/CPN-3 (SCR-620 or YK) and AN/CPN-6 Microwave Racon

Beacon Signal on B Scope
Beacon Signal on "B" Scope

DESCRIPTION: Microwave fixed ground or shipborne racon, transmitting coded identification signals when triggered by radar in plane.
USES: For homing friendly planes to their bases, and as a general navigation aid. AN/CPN-3 works with SCR-520, SCR-720, SCR-517, SCR-717, ASC and ASB airborne sets. AN/CPN is a microwave racon with essentially the same characteristics as AN/CPN-3, except that AN/CPN-6 works with SCR-717-T3, ASD, AIA, AN/APS-4 (ASH), AN/APS-3 (ASD-1) and AN/APS-15.
PERFORMANCE: AN/CPN-3's reliable maximum range is 100 mi. Range accuracy, ± 5%. Azimuth limits: 360°.
TRANSPORTABILITY: Without generator, AN/CPN-3 is crated in 5 units weighing 1,000 lbs. Largest is 24" x 24" x 48" and weighs 400 lbs. With generator, set is packed in 6 units, weighing 1500 lbs. Largest package is 44" x 33" x 26" and weighs 475 lbs.
INSTALLATION: Antenna should be mounted as high as practicable above surrounding terrain, or on highest part of ship. Since antenna location is critical, a competent engineer should select site. Three trained men can install and adjust equipment in a day on a ship, or 3 hours on shore.
PERSONNEL: No operator is required, but maintenance man should make 10-minute check every 4 to 8 hours. Consideration is being given to continuous monitoring in view of importance of navigational facilities provided.
POWER: AN/CPN-3 requires about 1000 watts AC, supplied by any 50-70 cycle 115-230 v. AC source, or by gas engine driven generator furnished on request. Generator uses standard 70-80 octane gas at rate of 0.65 gals. per hour.

* Available for issue in latter part of 1943.


*AN/TPN-1 and *AN/PPN-1 Light Weight Long Wave "Eureka" Racons

AN/PPN-1 in Paratroop Operations
AN/PPN-1 in Paratroop Operations

DESCRIPTION: AN/TPN-1 is a light-weight transportable airdrome homing racon; AN/PPN-1 is a very light-weight paratroop pack-set racon. Five transmitting frequencies and 5 receiving frequencies are available. Sets transmit when interrogated by AN/APN-2.
USES: For homing AN/APN-2 equipped aircraft to an airdrome, or to a predetermined spot for paratroop dropping, ground support, etc.
PERFORMANCE: When used with AN/APN-2, AN/APN-1 has a reliable maximum range of 50 miles at 2500 feet; AN/PPN-1, of 30 miles at 1500 feet.
TRANSPORTABILITY: AN/TPN-1 weighs about 150 lbs., complete, and is air transportable. AN/PPN-1 weighs about 30 lbs., complete, and can be carried in pack of paratroopers.
INSTALLATION: Ground location chosen by tactical requirements. AN/TPN-1 can be transported by motor vehicle, and set up by one man in from 15 minutes to an hour, depending on accessibility of antenna location. The 9-ft. antenna should be erected on as high a point as practical, in order to clear surrounding terrain. AN/PPN-1 is set up by paratrooper on as high as site as possible at location where other troops are to be dropped. Set-up time is about 10 minutes.
PERSONNEL: AN/PPN-1 is operated by one man. AN/TPN-1 requires no operator, but should be checked by maintenance personnel every 8 hours. (Six maintenance men are assigned to a Troop Carrier squadron for servicing all radar equipment.)
POWER: Power requirements of some AN/TPN-1 sets are supplied by 24-v. storage battery; others use 110-v. power source. AN/PPN-1 requires 15-20 watts from self-contained batteries, sufficient for 6 to 8 hours' operation.

* Available for issue in latter part of 1943.


*AN/APN-2 Airborne Long Wave "Rebecca" Interrogator-Responsor

AN/APN-2 in Troop Transport
AN/APN-2 in Troop Transport

DESCRIPTION: Airborne interrogator-responsor, with modified "A" indication, showing range and relative azimuth of the transpondor. Five transmitting frequencies and 2 receiving frequencies are available.
USES: For interrogating and homing on AN/TNP-1 and AN/PPN-1 transpondors.
PERFORMANCE: Line-of-sight range up to a maximum of 50 miles on AN/TPN-1 transpondor. Reliable maximum range of 30 miles on AN/PPN-1. Both sets have range accuracy of ± 5%, azimuth accuracy of ± 5°.
TRANSPORTABILITY: Set is shipped in 5 boxes, with a total crated weight of approximately 100 lbs. and a total crated volume of 10.22 cu. ft. Largest unit is the receiver-transmitter, 121/2" x 81/2" x 121/4", with a weight of 34 lbs., and a crated weight of 42 lbs.
INSTALLATION: Installed in troop carrier planes. Installed weight is 85 lbs.
PERSONNEL: AN/APN-2 is operated by plane's radio operator or navigator, and serviced by one of 6 radar maintenance men assigned to Troop Carrier Squadron.
POWER: 180 watts, 115 v., 400 cycles, AC, and 10 watts, 24 v., DC. from plane's DC supply and generators.
* Available for issue in latter part of 1943.


LORAN Long-Range Navigation System

Shipborne Receiving Equipment
Shipborne Receiving Equipment
Airborne Receiving Equipment
Airborne Receiving Equipment

DESCRIPTION: Long wave, long-range precise navigational system, comprising shore-based transmitters, and shipborne or airborne receivers.
USES: For navigation of ships and planes.
PERFORMANCE: Maximum range for ships is about 700 nautical miles by day and 1400 nautical miles by night; for planes, about the same as for ships over sea water but only 250 miles over land by day and 1200 miles over land by night. Accuracy varies, but the maximum total error of fix will seldom be as large as 1% of the mean distance from the transmitting stations. Maximum accuracy is about 1 or 2 miles.
TRANSPORTABILITY: Transmitting equipment is large and bulky, several carloads being necessary. Shipborne receivers are crated in 1 or 2 boxes; largest is 31" x 25" x 22" and weighs about 225 lbs. Airborne receivers (AN/APN-4 or SCR-622) are in 4 boxes; largest of 24" x 14" x 10", and total shipping weight is about 90 lbs.
INSTALLATION: Transmitting stations must be units in a chain of stations. selection of areas to be served by the Loran system is made under the cognizance of the Joint Chiefs of Staff; installation, maintenance, and operation of the stations at present are the responsibility of the Navy and Coast Guard. Shipborne receiving equipment weighs 120 lbs. installed; airborne receiving equipment, about 71 lbs. with cables.
PERSONNEL: Transmitting stations require a normal operating crew of from 10 to 15 operators and maintenance men for 24-hour service. Receivers are operated by the plane's or ship's navigator.
POWER: Single-pulsed transmitting station requires 5 KW, 110/220 v., 60 cycles, AC, from motor generator furnished with set. Double-pulsed stations, complete with standby equipment, require 10 to 15 KW. Shipborne receiver requires 240 watts from 110 v. 60 cycles, AC; airborne receiver, 240 watts from 110 v. 400 cycles, AC.


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