IFF--Identification Sets

--89--

Introduction to IFF

Image showing transponder, and interrogator-responsor.

IFF is an abbreviation of the phrase "identification of friend or foe." Since radar is used to direct gun fire or bombing at night, or in daylight when the target is beyond the range of visibility, it is obviously important that there be radar equipment that will serve to identify instantly any aircraft or ship as friend or foe before attack.

There are two basic components in any identification system at present in use: (1) the transpondor, carried by the aircraft or ship to be identified; (2) the interrogator-responsor, or questioning device, located aboard a ship, at a ground station, or in another aircraft.

The transpondor on a plane (or ship) is a combination radio transmitter and receiver, packaged in one small box. Normally, the transpondor is in a receiving condition, and will continue to function as a receiver until it receives a radio signal. Then, the transpondor will automatically become a transmitter and, as such, will transmit a signal in reply to that received. (The transpondor is said to have been triggered.)

In the identification systems now in use the transpondor when functioning as a receiver mechanically sweeps a band (or bands) of frequencies within a few seconds. If during a sweep through the

Image showing transponder and interrogator-responsor.

--90--

frequency band a radio signal within that band is received, the transpondor will send back the received signal within a fraction of a second, and will transmit the signal on the same frequency on which the signal was received. In effect, then, the transpondor acts as a selective mirror to radio signals.

The interrogator-responsor is also a transmitter and receiver. The transmitter (interrogator) is designed to permit triggering a transpondor. The receiver (responsor) gets the automatic transmitted reply from the transpondor, and by means of additional equipment displays this transmitted reply on a radar scope.

Two IFF systems are in use at present by American and British forces. They are:

(1)    IFF Mark II, and
(2) IFF Mark III.

Both systems use the same basic components--an airborne (or shipborne) transpondor, and an interrogator-responsor (which in the Mark II system is the search radar)--and operate on the same principle. The basic difference between the Mark II and Mark III systems is that the Mark III is a universal system.

The Mark II transpondors alternately sweep two or three bands of frequencies, but their bands are not common to all transpondors. Mark III transpondors sweep only one band of frequencies. The reason for this difference between the transpondors becomes obvious when their interrogators are examined.

Mark II System

In general, the Mark II system's interrogator-responsor unit is the ground, shipborne, or airborne search radar set. In the Mark II system there is no separate interrogator-responsor (IR) unit -- the regular radar search equipment, without any extra gadgets, serving as an interrogator-responsor.

Use of the Mark II system has required the airborne transpondors to be capable of replying to all types of radar interrogation employed throughout the various operational areas.

The multiplicity of radar frequencies now being used presents definite limitations to the successful operation of the Mark II system. However, its use continues as an interim measure until all British and American forces are equipped with the several components necessary to operation of the Mark III system.

Mark II Scope Display

Image showing normal signal from plane and IFF signal.
IFF Mark II and SC-1

Since the radar set alone performs the interrogator-responsor function in the Mark II system, the transpondor is triggered (i.e., automatically transmits) each time the transpondor sweeps through the frequency of the interrogating radar. When the transpondor has been triggered, the operator of the interrogating radar will observe on his scope a signal similar to a strong echo at the same or a slightly greater range than the echo made by the reflecting object itself.

The transpondor sweeps through the frequency of the interrogating radar once every six seconds. Because of the regular recurrence rate of the transpondor's signal (echo), this signal is recognized by the radar operator as an IFF reply.

A typical IFF Mark II scope presentation on an AC-1 radar set is pictured above.

--91--

Mark III System

In the Mark III system, identification is accomplished on a single band. This universal Mark III band is designated as "A" band by the Navy, and "I" band by the Army.

The Mark III system requires special interrogator-responsor equipment to be installed to supplement practically all radar sets. Installation of this IR equipment is arranged so that the IFF reply from a transpondor is shown on the interrogating radar's scope.

Scope presentations vary in the Mark III system. But no IFF signal appears on the radar scope until the interrogator key (challenge switch) has been pressed by the radar operator, unless it so happens that the radar frequency lies within the Navy's A (Army's I) band. Below is a picture of an IFF Mark III presentation on the A scope of an SM radar or an SCR-270 radar.

Image of A Band SM indicating enemy plane, normal signal from plane and IFF signal from plane.

After the interrogator key has been pressed by the operator, he then observes that the radar pips denoting friendly planes have corresponding identification pips appearing downward. Therefore, all radar pips not having an identification pip below denote unidentified planes. (On some radar sets the display splits into two, as shown in the picture above). Further substantiating evidence must generally be presented before the term "enemy" can be appended to unidentified planes.

The Mark III reply may be coded to provide additional security and identify special missions.

Mark III G Band

Besides the universal Mark III band, the Mark III system also has a G band reply for fighter planes only. The Navy A band (Army I) transpondor serves to identify all aircraft (including fighters) as friend or foe on the interrogating radar's scope; the G band transpondor further identifies friendly fighter aircraft on the interrogating CGI (SCI) radar's PPI scope.

Reason for the extra G band is that in GCI or SCI work it is often vital to segregate friendly fighters from other friendly or enemy craft so as to organize an interception. The PPI, of course, is the scope used in directing GCI work. How a G band reply appears is shown below.

Image of G Band SM indicating enemy plane or friendly bomber and friendly fighter plane.

The IFF Mark III G band display is shown only in response to a vocal request from the GCI station. The fighter plane pilot then turns a switch that causes a pattern similar to the one above to appear on the PPI. The IFF signal is symmetrical about the azimuth of the friendly plane. The friendly bomber or enemy plane shown on the above scope at the same range as the friendly fighter is thus distinguished the identity of other planes must be determined on the radar's A scope.

--92--

Interrogators and responsors are invariably used together. In some cases, too, interrogator, responsor and transpondor are all combined in a single unit; this system being known as IRT.

In addition to serving for identification purposes, IFF equipment has other special applications.

One of these is for racon interrogation by planes not equipped with search radars or equipped with search radars of a frequency not suitable for beacon interrogation. The frequency band covered by the IFF Mark III system makes it possible for airborne IR's (SCR-729 and AN/APX-2) to interrogate radar beacons covering the same frequency band, as is indicated in the description of these IR equipments in this book.

Image of Beacon Response  SCR-729 indicating range, on course (equal pips) and off course (unequal pips).
The SCR-729 can home on these radar beacons because it is installed with antennas suitable for lobe switching and the resulting pip matching needed in homing, as well as with an indicator needed for displaying the homing signals (see picture above).

AN/APX-2 can be adjusted for homing on beacon signals by employing a similar antenna system plus a lobe switching motor and a display device. The display device and switching motor used for this purpose is the AN/APA-1.

When a radar beacon is carried in a plane so that other aircraft can home on the plane, the beacon is called a rooster.1 A typical rooster operation is shown below -- the scout plane pilot calling other planes from the carrier while continuing to shadow the enemy convoy.

Image showing enemy convoy, scout plane with rooster and US task force.

Any airborne transpondor can be used as a rooster (1) if it has a fixed or spot frequency band, such as AN/APX-1 or the more versatile AN/APN-8, or (2) if the arm in the equipment that causes the sweep is removed. Since homing is done by pip matching, as is illustrated above [top image], rooster operations are difficult with the ordinary IFF transpondors that sweep a relatively wide frequency band at a slow rate.

The AN/APX-2 plus the AN/APA-1 when installed in a plane will serve the following functions: (1) transpondor; (2) IR; (3) rooster response so other planes can home; (4) rooster interrogation to home on another plane; (5) or (depending upon interrogating frequency) interrogation and response from YH (SCR-621) or YJ racons. Similarly the SCR-729 plus the SCR-695 (weighing about 1/3 more) will serve the same functions except for (3) above.

A final application of IFF is in aiding a plane in distress. A switch (marked "emergency") is provided so that when turned by the pilot the IFF replies with a distinctive and extra wide pulse -- thus allowing friendly planes to recognize and home on the disabled plane.


1. For other types of beacons see RACON in glossary at end of book.

--93--

NOTE:

In possible future editions of this publication, it is hoped that full information on the designations of british as well as U.S. IFF equipment will be given, and British units which will work with corresponding U.S. units will be catalogued in full. In what follows, correct but incomplete information of this sort has been attempted. Equipment of the Royal Navy and of the Royal Air Force is listed, not always completely, and all equipment of the British Army is omitted.

--94--

SCR-535 or ABE, & ABD Mark II Airborne Transpondors

DESCRIPTION: IFF Mark II airborne transpondors which alternately sweep two frequency bands providing uncoded radar response to challenges within their two frequency bands. These transpondors are basically the same, differing only in frequency range of one band.
USES: For identifying friendly plane to ground or ship radar stations ABD responds to following search radars:

    Royal Navy 286, 286M, 286P, 290, 291, 241.
    Army (Ground) SCR-270, SCR-271, SCR-268, SCR-545, SCR-527, SCR-588, SCR-602, SCR-627.
    Navy (Ship) SD, CXAM, SC, SA, SK.
    Navy (Airborne) ASE, ASVC.
    Army (Airborne) SCR-521-A, SCR-521-B, SCR-540-A.

ABD responds to following Airborne Interrogator-Responsors:

    Navy AN/APX-2
    Army SCR-729

ABE responds to following search radars:

    Royal Navy 79, 279, 286, 286P, 290, 291, 241, 286M.
    Army (Ground) SCR-268, SCR-545, SCR-527, SCR-588, SCR-602, SCR-627.
    Navy (Ship) CXAM, SC, SA, SK.
    Navy (Airborne) ASE, ASVC.
    Army (Airborne) SCR-521-A, SCR-521-B, SCR-540-A.

ABE responds to following Airborne Interrogator-Responsors:

    Navy AN/APX-2.
    Army SCR-729.

PERFORMANCE: Maximum range is 75 miles; minimum, 1 mile.
TRANSPORTABILITY: Sets (including spares) are packaged for shipment in 4 units, weighing a total of about 100 lbs. Largest unit is 15" x 15" x 30" and weighs about 45 lbs. One set of test equipment is supplied with every 10 sets.
INSTALLATION: Installed weight is 45 lbs.
PERSONNEL: In operation sets normally require only turning on and off by pilot. (see SD158). One maintenance man per squadron is needed.
POWER: Primary power required is 12 v., 5 amps. or 24 v., 2.5 amps., DC, depending on model used. Source is plane's battery and generator system.

--95--

SCR-595, ABK or BK Mark III Airborne or Shipborne Transpondors

DESCRIPTION: IFF Mark III Airborne transpondor which sweeps a single band of frequencies (designated by the Navy as the A band and by the Army as the I band) and provides a coded reply for reception by a responsor throughout the band. Adapted to ship use with motor generator and type 66-ACG antennas.
USES: For identifying friendly planes or ships to properly equipped aircraft, ship, or ground stations. ABJ responds to:

    Navy (Ship) Interrogator-Responsors BL, BN, BM; Radars SC, SA.

    Army (Ground Interrogator-Responsors RC-107, RC-127, RC-136, RC-145, RC-148, RC-150, RC-151, RC-157, RC-182, RC-184, RC-188, RC-192, RC-215, RC-282.

    Royal Navy Interrogator-Responsors 242, 243.

    Navy (Airborne) Interrogator-Responsors AN/APX-2; Radars ASE, ASVC.

    Army (Airborne) Interrogator-Responsors SCR-729; Radars SCR-521-A, SCR-521-B.

PERFORMANCE: Maximum reliable range is 90 miles, (125 miles using RC-150 or RC-151). Minimum range is 1 to 10 miles, depending on the associated interrogator.
TRANSPORTABILITY: Set is packed for shipment in 4 units, weighing approximately 100 lbs. Largest package is about 15" x 15" x 30" and weighs about 45 lbs. Navy supplies one test equipment with every 10 sets. Army supplies 4 test equipments to a fighter squadron, 3 to a light dive bomb squadron, and 2 for all other squadrons.
INSTALLATION: Installed weight is 60 lbs. plus a 214-lb. motor generator when installed on ship.
PERSONNEL: In operation, set normally requires only turning on and off by pilot or operator (see SD158). Navy sets are serviced by regular radar maintenance personnel. Army recommends 4 maintenance men per fighter squadron, 3 per light/dive bomb squadron, and 2 for all other squadrons.
POWER: Required primary power is 12 v., 10 amps., or 24 v., 5 amps., DC, depending on model used. Source is plane's battery and generator system or motor generator on ships.

--96--

SCR-692 or ABF Mark III Airborne Transpondor

DESCRIPTION: IFF Mark III airborne transpondor similar to the ABK in that it sweeps the Navy A band frequencies (Army's I band) providing a coded reply for reception by a responsor upon being challenged on a frequency in the band. In addition to this function, the SCR-695 is provided with a second transpondor which operates on a fixed frequency that may be adjusted over a range designated as the G band. This G band transpondor provides a frequency channel for interceptors operating with ground and shipboard GCI units.
USES: The A Band transpondor serves to identify the aircraft as friendly and its G band transpondor further identifies the aircraft as a fighter directly on the GCI PPI indicator. SCR-695 (ABF) responds to:

    Navy (Ship) Interrogator-Responsors BL, BN, BM, BO; Radars SC, SA.

    Army (Ground) Interrogator-Responsors RC-107, RC-127, RC- 36, RC-145, RC-148, RC-150, RC-151, RC-157, RC-182, RC-184, RC-188, RC-192, RC-215, RC-282; Radars SCR-527, SCR-545, SCR-588, SCR-602, SCR-627.

    Royal Navy Interrogator-Responsors 242, 243.

    Navy (Airborne) Interrogator-Responsors AN/APX-2; Radars ASE, ASVC.

    Army (Airborne) Interrogator-Responsors SCR-729; radars SCR-521-A, SCR-521-B.

PERFORMANCE: Reliable maximum range is 90 miles (125 miles with RC-150 or RC-151). Reliable minimum range is 1 to 10 miles, depending on associated interrogator.
TRANSPORTABILITY: Set is packed for shipment in 1 unit weighing a total of 45 lbs., plus Group A parts shipped in bulk. Largest unit is about 15" x 15" x 30" and weighs about 50 lbs. Navy supplies one test equipment with every 10 ABF sets; Army supplies 4 test equipments to a fighter squadron, 3 to a light/dive bomber squadron and 2 to all other squadrons.
INSTALLATION: Installed weight is 60 lbs.
PERSONNEL: Set normally requires only turning on and off and occasionally switching operation by pilots (see SD158). Navy sets are serviced by regular radar maintenance personnel. Army recommends 4 maintenance men per fighter squadron, 3 per light/dive bomb squadron and 2 for all other squadrons.
POWER: Primary power required is 10 amps., 12 v. DC (for model SCR-695-AZ) and 5 amps., 24 v. DC (for model SCR-695-A and ABF), from plane's battery and generator system.

--97--

*AN/APX-1 Mark III Airborne Transpondor

DESCRIPTION: IFF Mark III airborne transpondor similar to the SCR-695. Its G band frequency determining unit is replaceable which permits a larger band of frequencies to select from. It is provided with facilities for operation as an airborne radar beacon (rooster) on any fixed frequency within the G band.
USES: For use in fighter aircraft to enable ground and shipboard fighter director units to identify aircraft so equipped as friendly fighters. For use in patrol and scout aircraft to furnish a beacon response to friendly radar equipped aircraft. AN/APX-1 responds to:

    Navy (Ship) Interrogator-Responsors BL, BN, BM, BO: Radars SC, SA

    Army (Ground) Interrogator-Responsors RC-107, RC-127, RC-136, RC-145, RC-148, RC-150, RC-151, RC-157, RC-182, RC-184, RC-188, RC-192, RC-215, RC-282; Radars SCR-527, SCR-545, SCR-588, SRC-602, SCR-627.

    Royal Navy Interrogator-Responsors 242, 243.

    Navy (Airborne) Interrogator-Responsors AN/APX-2; Radars ASE, ASVC.

    Army (Airborne) Interrogators-Responsors SCR-729; Radars SCR-521-A, SCR-521-B. In addition works as an airborne radar beacon (rooster) and will respond as such to ASE, ASVC, SCR-521-A and SCR-521-B.

PERFORMANCE: Reliable maximum range is 90 miles; minimum range, 1 mile.
TRANSPORTABILITY: Set is packed for shipment in 4 units, weighing approximately 100 lbs. Largest unit is about 15" x 15" x 30" and weighs about 45 lbs. Spares and test equipment are included.
INSTALLATION: Installed weight is about 50 lbs.
PERSONNEL: Set normally requires only turning on and off, plus occasional switching operations. This is done by the pilot in single-seated fighters, or by the radar operator in multi-placed planes (See SD-158). One maintenance man per squadron is required.
POWER: Required primary power of 5 amps. 24 V or 11 amps. 12 V DC is from plane's battery and generator system.

* Available for issue in latter part of 1943.

--98--

*AN/APX-2 (ABJ) Mark III Airborne IRT

DESCRIPTION: IFF Mark III airborne combination Interrogator-responsor-transpondor. As a transpondor and radar beacon (rooster), this equipment is identical to the AN/APX-1. In addition, it is provided with interrogator-responsor facilities on any fixed frequency within the Navy A band frequency limits.
USES: For use in all search radar equipped aircraft. Its IFF transpondors permit aircraft so equipped to be identified as friendly by a ground, ship or aircraft fitted with an A band interrogator-responsor. As a radar beacon, it permits other radar equipped aircraft to home to it (assuming correct frequency adjustments). As an interrogator-responsor, it permits aircraft so equipped to identify as friendly all ships and aircraft fitted with any IFF Mark III A band transpondor. When utilized with a suitable antenna system, the AN/APX-2 may be used to interrogate and home to ground radar beacons operating within the limits of the A band frequencies. Operation of the AN/APX-2 is also possible in aircraft not fitted for radar. This may be accomplished by the utilization of the indicator (display) unit of the SCR-729 or the ASE remote indicator AN/APA-1. AN/APX-2 respond to:

    Navy (Ship) Interrogator-Responsors BL, BN, BM, BO; Radars SC, SA.

    Army (Ground) Interrogator-Responsors RC-1097, RC-127, RC-136, RC-145, RC-148, RC-150, RC-151, RC-157, RC-182, RC-184, RC-188, RC-192, RC-215, RC-282; Radars SCR-527, SCR-545, SCR-588, ASCR-602, SCR-627.

    Royal Navy Interrogator-Responsors 242, 243.

    Navy (Airborne) Interrogator-responsors AN/APX-2; Radars ASE, ASVC.

    Army (Airborne) Interrogator-responsors SCR-729; Radars SCR-521-A, SCR-521-B.

In addition, as an Interrogator-responsor it will interrogate for reply any ship or airborne Mk III IFF "A" band transpondor, such as BK, ABK, SCR-595, SCR-695, AN/APX-1, AN/APX-2, RAF-3090, 3120, 3121, and rn-253. As an airborne beacon (rooster) responds to ASE, ASVC, SCR-521-A and SCR-521-B.

PERFORMANCE: Reliable maximum range for transpondors is 90 miles; for interrogators and responsors, 60 miles. Minimum range is 2 miles.
TRANSPORTABILITY: Set will be packed for shipment, with spares and testing equipment in 4 units. Total weight will not exceed 100 lbs.
INSTALLATION: Installed weight of set is 52 lbs.
PERSONNEL: Set will be operated by the pilot in single-seated aircraft, or by the radar operator in multi-place planes. One maintenance man per squadron is recommended.
POWER: Required primary power is 115V, 400-2400 cycles at 150 watts, plus 25 watts DC at 24 V.

* Available for issue in latter part of 1943.

--99--

*AN/APA-1 Pilot Repeat Indicator

DESCRIPTION: Pilot repeat indicator for any ASB or ASE radar, or for IFF Mark III interrogator-responsor-transpondor AN/APX-2, or for some forms of SCR-729.
USES: When used with search radar, provides navigational and tactical data to pilot. Used as a blind bombing aid in conjunction with ASB. For IFF application, AN/APA-1 provides separate display for identification of other aircraft, racon and rooster homing facilities.
PERFORMANCE: Corresponds to that of associated search radar or IFF IR unit.
TRANSPORTABILITY: Shipment, including operating spares, is packed in one or two units.
INSTALLATION: Installed weight is 35 lbs.
PERSONNEL: Indicator is used by pilot, or by radar operator in some applications, and serviced by regular radar maintenance personnel.
POWER: Required primary power is 85 watts, 115 V, 400-2400 cycles AC, plus about 20 watts, 20-30 V, DC.

SCR-729 Mark III Airborne IR

DESCRIPTION: IFF Mark III airborne interrogator-responsor.
USES: When operated with a suitable antenna system, its installation permits aircraft so equipped to challenge and identify as friendly aircraft and ships equipped with any Navy A or Army I band transpondor. In addition, it may be used to interrogate and home on YH, YJ and SCR-621 radar beacons, and on BABS beach approach beacon of the R.A.F. Works with ABK, AN/APX-1, AN/APX-2, SCR-695 and SCR-595, RAF 3067, 3090, 3120, and 3121; Royal Navy 253. Display of identification or homing facilities may be obtained on SCR-729 "A" scope or the scope of the associated radar equipment.
PERFORMANCE: Reliable maximum range is 60 miles, minimum range is 20 miles. Azimuth limits are 80° forward, with accuracy (when homing on beacon) of ± 2°. Elevation limits are 40° forward.
TRANSPORTABILITY: Set is packed for shipment in 5 units, weighing a total of about 190 lbs. Spares and testing equipment are included.
INSTALLATION: Installed weight is 150 to 115 lbs., depending on type of antenna used.
PERSONNEL: Set requires on operator, who may be the regular radar operator or a specially trained radio operator. One maintenance man per squadron is needed.
POWER: Required primary power is 150 watts, 115 v., 400-2400 cycles, plus 25 watts DC at 24 v. (for SCR-729-A) or 25 watts DC at 12 v. (for SCR-729-AZ.)

* Available for issue in latter part of 1943.

--100--

*AN/APN-8 Airborne Radar Transpondor Beacon

DESCRIPTION: Airborne radar transpondor beacon. The main units has the same form factor as the ABK and is interchangeable in the ABK shock mount.
USES: Set is an airborne version of the YJ ground radar and consists of two transpondors that receive and respond on different frequencies. Permits planes equipped with SCR-517, SCR-521, ASV, ASVC, ASE and ASB to home on it. Also, planes fitted with centimeter-type radars (or no radars at all) may home on it if the planes are provided with AN/APX-2 with suitable antennas and accessories (AN/APA-1) or SCR-729.
PERFORMANCE: Reliable maximum range: 60 miles; reliable minimum, 2 miles. Range accuracy is 0.2 miles. Azimuth and elevation accuracy is determined by interrogator.
TRANSPORTABILITY: Shipment includes spares for 1000 hours operation, testing equipment and separate generator if needed. Complete shipment is packed in 3 units and weighs about 90 lbs. Largest package is 15" x 15" x 20" and weighs 40 to 50 lbs.
INSTALLATION: Installed weight is approximately 60 lbs.
PERSONNEL: Radio or radar operator.
POWER: Requires primary power of 200 watts DC at 12 or 24 volts. Source is plane's battery. A dynamotor is supplied.

BL and *BM Mark III (A Band) Shipborne IR

DESCRIPTION: IFF Mark III (A band) shipborne interrogator-responsor. BM is improved version of BL.
USES: Interrogates Mark III transpondors (ABK, SCR-595, SCR-695, ABF, AN/APX-1, AN/APX-2) and gives an IFF reply on the radar scope.
PERFORMANCE: Reliable maximum ranges: for BL, 90 miles; for BM, 100 miles is expected.
TRANSPORTABILITY: Shipments of both sets include spares. BM has testing equipment as integral part. BL is packed for shipment in 2 units and weighs when crated a total of 375 lbs. BM is packed in 3 packages. Both sets are air transportable.
INSTALLATION: BL has 4 components weighing a total of approximately 274 lbs. The equipment component is 20" x 30" x 203/4" and weighs 250 lbs. BM has 2 components, weighing a total of 585 lbs. The equipment component is 30" x 20" x 203/4" and weighs 275 lbs.
PERSONNEL: Usually no additional personnel required -- the associated radar personnel serving.
POWER: Primary power required is 300 watts for BM, and 400 watts for BL, 110 v AC, 60 cycles. Source is ship's power or supply of associated radar.

* Available for issue in latter part of 1943.

--101--

BN Mark III (A Band) Low Power Shipborne IR

DESCRIPTION: IFF Mark III (A band) low-power shipborne interrogator-responsor.
USES: RN is designed primarily for small ships and boats for use with surface search and fire control shipborne radars. It interrogates Mark III transpondors (chiefly ABK) and gives IFF reply to the radar indicator.
PERFORMANCE: Reliable maximum range is approximately 50 miles, ship to plane.
TRANSPORTABILITY: Complete shipment includes spares and is packed in 4 units. Can be carried in any transport plane.
INSTALLATION: BN has 2 components: equipment (1911/16" x 167/16" x 143/8") that weighs 150 lbs., and the antenna which should be installed as high as possible.
PERSONNEL: Usually no additional personnel is required -- the associated radar personnel serving.
POWER: Primary power required is 225 watts, 110 volts AC, 60 cycles. Source is ship's supply.

*BO Mark III (G Band) High Power Shipborne IR

DESCRIPTION: IFF Mark III (G band) high-power shipborne interrogator-responsor. Contains test monitor equipment.
USES: Interrogates G band (fighter direction) transpondors (SCR-695, ABF, AN/APX-2 and AN/APX-1) and receives IFF reply. For use with SM radars.
PERFORMANCE: Reliable maximum range is about 90 miles.
TRANSPORTABILITY: Shipment includes spares, and is air transportable in any transport.
INSTALLATION: BO has 2 components: equipment (30" x 20" x 203/4") which weighs 275 lbs. and antenna array which weighs 85 lbs. and is mounted on SM antenna.
PERSONNEL: Usually no additional personnel is required -- the associated radar personnel serving.
POWER: Primary power required is 300 watts, 110 volts, 60 cycles. Source is ship's power or supply of associated radar.

* Available for issue in latter part of 1943.

--102--

MARK III IR's for Army Ground Equipment -- I

DESCRIPTION: Army IFF Mark III Interrogator-Responsors: RC-148 for SCR-268, RC-150 for SCR-270, RC-151 for SCR-271, RC-316 for SCR-516. Contains transmitter, receiver, interconnecting unit to radar display and antenna mounted on radar antenna.
USES: To interrogate airborne IFF Mark III transpondors: IFF Mark III, Navy ABK, SCR-595; IFF Mark III-G, SCR-695, Navy ABF; AN/APX-1&2.
PERFORMANCE: Range of IFF approximately the range of the radar.
TRANSPORTABILITY: Approximate average weight of these sets, when packaged for shipment, is 2160 lbs. Approximate number of units per set is 13, largest of which will measure about 59" x 22" x 35". Shipment includes spares for 4 months.
INSTALLATION: Approximate installed weight is 1600 lbs.
PERSONNEL: RC-148, RC-150, RC-151 are operated and maintained by regular radar operating personnel.
POWER: 1200 Watts AC 60 cycle drawn from the power source of the associated radar.

MARK III IR's for Army Ground Equipment -- II

DESCRIPTION: Army IFF Mark III Interrogator-Responsors: RC-127 for SCR-527, RC-136 for SCR-296, RC-145 for SCR-545, RC-182 for SCR-582, RC-184 for SCR-584, RC-188 for SCR-588. Contain transmitter, receiver, antenna control display, tower and rotatable lobe switched antenna.
USES: To interrogate airborne IFF Mark III transpondors: IFF Mark III, Navy ABK, SCR-595; IFF Mark III-G, SCR-695, Navy ABF; AN/APX-1&2.
PERFORMANCE: Range of IFF approximately the range of the radar.
TRANSPORTABILITY: Approximate average weight of these sets, when packaged for shipment, is 5200 lbs. Approximate number of units per set is 16, largest of which will measure about 66" x 36" x 31". Shipment includes spares for 4 months.
INSTALLATION: Approximate installed weight is 3600 lbs.
PERSONNEL: IR sets listed above require an IFF operator and special maintenance men.
POWER: 1500 Watts AC 60 cycle drawn from the power source of the associated radar.

--103--

*Mark III IR's for Army Ground Equipment -- III

DESCRIPTION: Army IFF Mark III interrogator-responsors: RC-192 for SCR-602-T1, SCR-602-T6, SCR-602-A, AN/TPS-1, AN/TPS-3. Contains transmitter, receiver BC-800 (same as in SCR-729) control box, tower, transmitting and receiving vertical antennas.
USES: To interrogate Airborne IFF Mark III transpondors: IFF Mark III, Navy ABK, SCR-595, IFF Mark III-G, SCR-605, Navy ABF, AN/APX-1&2.
PERFORMANCE: Range of IFF approximately the range of the radar.
TRANSPORTABILITY: Data tentative: Approximate average weight of these sets when packaged for shipment is 500 lbs. Approximate number of units per set is 5, largest of which will measure about 14" x 14" x 60". Shipment includes spares for 4 months.
INSTALLATION: Approximate installed weight 300 lbs.
PERSONNEL: IR set is operated by regular radar operating personnel.
POWER: 125 watts AC 400-2400 cycle 80-115 volts and 10 watts 24 volts DC drawn from the power source of the associated radar.

* Available for issue in latter part of 1943.

--104--

Table of Contents
Previous Chapter (Navigation Aids) *  Next Chapter (Miscellaneous)