CRT-1B Expendable Radio SonoBuoy (ESRB)

© Brooke Clarke 2014

CRT-1B Sonobuoy
Fig 1
CRT-1 Description
ARR-3 Sonobuoy Receiver
ASQ-1 MAD equipment


A couple (GSQ-154, GSQ-160) of the outdoor Intrusion Detectors from the Vietnam era use cylindrical modules that seemed to come from sonobuoys so I tried to find the sonobuoy that was the source, but so far have not found it.  My Sonobuoy web page has information on a few buoys as well as Vietnam era equipment that was re-purposed for outdoor intrusion detection.  In the process of making that web page I learned that the CRT-1 was the first U.S. sonobuoy.

Sonobuoy transmits an FM modulated signal:
CRT-1A: 67.7 to 71.7 MHz
CRT-1B: 62.9 to 66.9 MHz
Used with the AN/ARR-3 twelve channel receiver. Used in conjunction with the AN/ASQ-1 MAD equipment.

In 1942 Magnetic Anomaly Detection (Wiki MAD) was invented (see Sonobuoy MAD patents) but it could not tell the difference between a sub near the surface and a much larger ship on the bottom.  The sonobuoy was the answer to that problem.  The CRT-1 was first put in service March 1942.  The CRT-1 could only detect a sub if the propeller was cavitating.  Under the best of conditions the range was about three and a half miles. (Wiki)Ref 1.

I believe this was used as the basis of the Project Mogul "flying disks" used to listen for atomic explosions and/or missile launch noises in the stratospheric sound channel.  For more on this see my Roswell Connection paragraph on the Sonobuoy web page.

I have another web page for Torpedoes, depth charges, mines and hedgehogs.

CRT-1 Description



Just under 40" tall with the antenna collapsed and eleven pounds without batteries or the shipping tube.  Tube is just over 4-1/4" diameter.

The telescoping antenna was frozen as received.  I've applied a few drops of Kroil and maybe tomorrow it will fully extend.

Surrounding the antenna at the top is a black plastic cylinder about 6" high and 2-5/8" diameter inside of which is a coiled up synthetic rope which I guess was attached to a parachute prior to deployment from an airplane.  It's marked MX-211/CRT-1A.  Note the "A" was not changed when the sonobuoy was upgraded.

The hydrophone appears to be made from some type of wire wrapped around a hollow ferrous cylinder 5" tall by 3" outside diameter.  It's connected to the main body by what looks like common household AC power line cord.  Normally it would be held inside the bottom of the tube but it came out when the sonobuoy was removed from the shipping tube and since the wire is now very stiff it would break into bits if forced back into the tube.


Fig 1 Overall
CRT-1B Sonobuoy

CRT-1B Sonobuoy shown outside the shipping tube.
Antenna all the way down.

The hydrophone has come out of the bottom and probably will not go back in because the wire is brittle.

Wire length said to be twenty four feet.
Fig 2 Top
CRT-1B Sonobuoy

The telescoping antenna has been pulled part way out.
Said to be about one meter long when extended.  A 1/4 wavelength antenna 1 meter long means a wavelength is 4 meters or about 75 MHz. (Mc back then).

At the left you can see a small black rubber plug.  Function unknown.

Rad Tag Reads:

Replace pin immediately
to conserve battery.
Note: tag connected to one of the parachute shouds and that shroud connected to short (1/2" long) pin that will be pulled when the parachute deploys.  In order to reinstall the pin a spring loaded plate needs to be moved to uncover the hole in the top.

Label reads:

NXsa-65296,  13415 :CABC
Fig 3 Main Label
CRT-1B Sonobuoy

Color <red>
NXsa-65283,  2805-CEX
Fig 4 Hydrophone (Wiki)
CRT-1B Sonobuoy

5" tall x 3" dia. Nickel cylinder wrapped with wire.  There's a permanent magnet inside the hydrophone (a nearby compass is strongly influenced).

NXsa 65283
Ser. 5717

  942897 Apparatus for receiving submarine sounds, Thomas Alexander Garrett, William Lucas, Dec 14, 1909, B06B1/08
               Magnetized Nickel rod develops voltage in coil & is more stable than carbon mike.
1811127 Balanced magnetostrictive oscillator, Harrison Jamison R, Wired Radio Inc, Jun 23, 1931,
331/157, 367/168, 331/59, 331/168, 318/118
               aimed at using magnetostrictive element to replace a quartz crystal, but a simple 2-tube oscillator circuit.

1882397 Magnetostrictive vibrator, Washington Pierce George, Oct 11, 1932, 333/201, 318/118, 361/206 -
               mechanical arrangements of magnets and material
Apparatus for transmission and reception, Leonard Steinberger Raymond, Dec 15, 1936,
               367/153, 318/118, 367/174, 181/164, 181/168
2166359 Magnetostrictive device, Lakatos Emory, Bell Labs, Jul 18, 1939 - basic info on Magnetostriction w/plots
               333/201, 420/581, 252/62.55, 148/312, 367/168, 420/459, 310/26, 148/315, 335/215, 318/118, 367/176
2328496 Magnetostrictive microphone, Mar 22, 1939, Yves Rocard, 367/168, 333/148, 335/215, 310/26, 381/190
2414699 Magnetostrictive signal translating apparatus, Rca Corp, Dec 30, 1944, 367/168, 310/26, 318/118
2415407 Submarine signaling apparatus, Hugo Benioff, Submarine Signal Co, Dec 9, 1942, Feb 11, 1947, 367/168
thin cylindrical shell 49 of magnetostrictive material..."
Art of tuning magnetostrictive elements, Rca Corp, Nov 29, 1944, 310/26, 318/118, 367/168
2435487 Electromechanical vibrator, Robert Adler, Zenith Radio Corp, Feb 1, 1943, Feb 3, 1948,
331/157, 335/215, 331/138, 331/107.00R, 335/224, 310/25, 310/113, 310/26, 335/229, 318/128, 335/221
                Although this device can provide mechanical vibrations up to 2.8 MHz using non ferrous materials, most
                of the implementations use magnetostrictive material (Fig 3 and up).  diagrams showing magnetic poles

Electroacoustical transducer, Turner Jr Edwin E, Submarine Signal Co, Nov 18, 1942, Mar 9, 1948,
                367/168, 381/182, 381/190 - uses permanent magnets for bias
2468270 Magnetostrictive transducer, Rca Corp, Dec 30, 1944, 367/168
2566984 Magnetostrictive device, George Firth Francis, Sep 4, 1951, 310/26, 165/84, 367/156, 366/127, 310/16
               although designed to generate ultrasonic with some power it would make a good microphone
Microphone, Filed: Sep 11, 1943, Granted: May 12, 1959,  367/168, 310/26, 114/25, 367/157, 381/190
Dual magnetostrictive hydrophone, Reginald A Hackley, Mar 29, 1946, Apr 11, 1961 (SECRET for 15 years),
367/156, 333/201, 181/165, 116/DIG.180, 381/427, 381/162, 310/26              
3509523 Helical-wound magnetostrictive line hydrophone, Parker David E, Prentice Winslow W, Us Navy, Apr 28, 1970, 367/168
              " ...
can be economically fabricated in a continuous manner to provide any desired length."
Magnetostriction (Wiki) -

The Maritime web page says this is how it works.

"...a cylindrical magnetostriction unit that is wound on a nickel shell. Its construction permits the storing of the cable inside the hollow shell and effects a reduction in length of about 4 inches compared with earlier models."

Fig 5 Tags at top of Antenna
CRT-1B Sonobuoy
Electronics Follow up and evaluation Tag (not filled in)

T.O. 49.49
2 each BA-51 (2 * 67.5V = 135 V B+)
4 each BA-30 (parallel connection 1.5V filament)

Ready for Issue Tag
Part No. AN/CRT-1B
Nomenclature: Transmitter
Stock No. R-16-T-9171
BU or Serial No. 2805 CEX
Fig 6
CRT-1B Sonobuoy
(not filled in)


(paper under staple) Nav??p 2650
Changes Incorporated
Change No. B50 40-49
Shop No. NASSD
Shop Insp. HK

Stamps 42(anchor)11, 42(anchor)30
Fig 7 Schematic of Transmitter
CRT-1 Sonobuoy
                  Transmitter schematic

The circuit shows an input jack and no DC bias on the transducer, so it may be working without any electrical bias, but there is a permanent magnet to provide the bias.
Fig 7 Electronics assembly
RCA jack in lower left is hydrophone input
CRT-1B Sonobuoy
Fig 8 Electronics assembly
Fig 9 Close-up Electronics assembly
T 1B/CRT-1
Clear plastic cylinder removed
Chassis plate is shock mounted
Tube on left is marked 3A4
Fig 10 Close-up Electronics assembly
Clear plastic cylinder removed
Tube on right is marked 1L4

ARR-3 Receiver

Used in aircraft.  Powered by 24 VDC.  The 12 Volt filament tubes are paired so filaments are powered by 24 VDC.  A "rotary transformer" supplies the B+.

ARR-3 Photos and information supplied by Michael, VK4ZKT

Fig ARR-3 #1  Front with 1629 Magic-Eye tube.
ARR-3 Sonobuoy
Fig ARR-3 #2 Back Inside
ARR-3 Sonobuoy
Fig ARR-3 #3 Bottom
FET converter PCB allows reception of FM broadcast
ARR-3 Sonobuoy
Description (pdf) with schematic
CRT-1 & ARR-3
                  Tech Information & schematic
2017 June 30  from eBay UK seller  jet-art-aviation
JetArt web page
ARR-3 Sonobuoy

ASQ-1 MAD equipment


1336497 receiver mounting for submarine signals - through hull microphone Apr 13 1920, 381/177; 381/412


1. Aircraft versus Submarine in two world wars by Dr. Alfred Price, 2004 (Price wrote Instruments of Darkness about ECM)
YouTube: Navy Depth Charge Demonstration (1946) 24/10/1946. FILM ID:2347.03 - Really about Sonobuoys and probably the CRT-1.  "Various tactical situations require different procedures and exact patterns.  Only by learning these and adhering to them can the full effectiveness of sonobuoys be realized".


Outdoor Intrusion Detectors
Torpedoes, depth charges, mines and hedgehogs.


Richard Muller Physics Lecture 11 - Waves 1 - W.W.II underwater channel and the Roswell connection - origin of the term "Flying Saucer".

PRC68, Alphanumeric Index of web pages, Products for SaleBrooke's Military Information 
page created 17 Dec 2014