The essential parts of JP gear


1. Hydrophone

When a sound wave hits the front of the hydrophone, the long metal tube changes slightly in size. This sets up an electric current in wires coiled around its wooden core. Sound cannot hit the back, of the tube very strongly because it is protected by a rubber bale.

  Photo of JP sound head.
2. Training mechanism

The shaft on which the hydrophone is mounted goes down through the pressure hull into the forward torpedo room. Inside the shaft a cable carries the electric current to the amplifier. Geared to the shaft is a training handwheel. One full turn of this wheel turns the hydrophone about 33 degrees. On the circular scale, the target's relative bearing is read opposite the pointer.

  Photo of training mechanism.
3. Amplifier

In the amplifier the electric current from the hydrophone is made stronger.

4. Headphones

By means of the headphones, or loudspeaker, the electric current from the amplifier is changed back into sound. Thus the operator can hear and identify sounds coming through the water.

Power supply. JP gets its power from the submarine's batteries. This has two advantages: First, there is no generator to make noise during silent running of the submarine. Second, even if depth-charge damage cuts off the submarine's main power supply, the JP operator can still tell what is happening on the surface.


This is the way


Block diagram of JP amplifier. First Amplifier Stage -> Second Amplifier Stage -> Bass Boost Filter, Flat Filter, 500-Cycle Filter, 3000-Cycle Filter, 6000-Cycle Filter -> Third Stage Amplifier Stage -> Fourth Amplifier Stage -> Output Amplifier Stage (with feedback Prop Count Detector) -> Transformer/Speaker, Headphone, Amplifier/Filter/Rectifier/Magic Eye Indicator

the JP amplifier works


1st amplifier stage receives the incoming electric current from the hydrophone and makes it stronger.

2nd amplifier stage makes this amplified current still stronger.


Bass-boost filter weakens frequencies above 1500 cycles, making the low frequencies seem stronger. Flat filter passes all frequencies equally well. 500-cycle filter cuts out frequencies below 500 cycles it weakens frequencies from 500 to 2500 cycles, making the higher frequencies seem stronger.
3000-cycle filter weakens frequencies below 3000 cycles, making the higher frequencies seem stronger. 6000-cycle filter makes 6000 cycles stand out by weakening frequencies lower and higher than this.
3rd amplifier stage makes the filtered current stronger. How much stronger is determined by the volume-control setting.

4th amplifier stage makes this amplified current still stronger.

Prop-count detector changes the current so that the propeller beats stand out.
Output amplifier stage makes the current strong enough for the headphones.
Transformer changes the current so that the loud speaker can handle it.

Loudspeaker changes the electrical current into sound.

Headphones change the electrical current into sound. Amplifier strengthens a small portion of the current. How much it is strengthened is determined by the indicator control setting.

Filter cuts out all frequencies below 6000.

Rectifier changes the current so that the indicator can handle it.

Magic eye indicator lets the operator's eye see what his ears hear. The eye closes when current is strongest.


These are the steps to take

Photo of JP amplifier.
1-Turn Power Switch On
2-Watch For Magic Eye To Glow
3-Turn Prop-Count Detector Switch OFF
4-Unscrew Cap From Magnetizer Jack. Plug Hydrophone Cable Into This Jack.
5-Press Push-to-Magnetize Button.  Wait 15 Seconds. Push It Again.

Power switch when ON, allows power to be supplied to the amplifier.

Input jacks. When the cable is connected to the hydrophone jack, the current from the hydrophone goes into the amplifier. When the cable is connected to the magnetizer jack, power from the amplifier can be sent into the hydrophone, magnetizing it to make it more sensitive.

  Push-to-magnetize button sends the magnetizing power into the hydrophone.

Prop-count detector. Sometimes you can get a better turn count with this ON.

Magic eye indicator. The eye closes when the hydrophone is trained exactly on the loudest sound.


in starting JP sonic listening gear

Photo of JP amplifier.
6-Unplug Cable From Magnetizer Jack. Replace Cap.
7-Plug Cable Into Hydrophone Jack.
8-Turn Volume To Zero.
9-Plug Headpphones Into Phone Jack.
10-Set Volume At A Comfortable Level For Listening, Water Noise Not Too High.
11-Turn Filter Control To 500 and Listen.  If Background Noise Is Low, Turn To Flat; If High, Turn to 3000. Search On Lowest Position Background Noise Permits.

Phones jack. Headphones are plugged in here for normal operation.

Speaker jack. If speaker is used, it is plugged in here.

Fuse. If a fuse burns out, your gear will go dead. Call the radio technician.

  Volume control. As this is turned clockwise, the sound is made louder.

Filter control selects whichever of the five filters you want to use.

Indicator control. Turned clockwise, this increases the strength of the current going to the magic eye.


JP Search Procedures
When you are on sonar watch, until you get a contact, your time will be spent in routine searching. To get the proper rate of sweep, you will have to turn the handwheel rapidly. When you take over the watch, you first carry out ...
Rapid search

1. From the bearing at which the hydrophone was left by the previous watch, sweep through 000 degrees and continue on to 180 degrees.

2. Then, reversing direction, sweep back around the full circle to 180 degrees. If no suspicious sounds are heard, shift to ...

  Illustration of rapid search.
Progressive search

Sweep forward two full turns of the handwheel and then one turn back. Continue up the same side, two turns forward and one turn back, until you have crossed the bow. Then train rapidly down the opposite side to 180 degrees. Reverse direction and train two turns forward, one back, two forward, one back, until you have crossed the bow again. Then train rapidly down the other side ... and so on. Continue this procedure for the duration of your watch, unless ordered to do otherwise.

Illustration progressive search.


These are some of the sounds you are likely to hear


Illustration sources of noise from enemy ships.   Report these sounds

1. Enemy ships' propellers have rhythmic, swishing beats. PT boats whine and freighters chug.

2. Enemy ships' machinery noise is not rhythmic like propellers. For example, generators sound just as you would expect.

3. Enemy echo-ranging (pinging) produces dull thuds or sometimes shrill peeps on JP.

4. On your own submarine, electric motors have a smooth hum; bow planes grate; the TDC whirrs; blowing tanks make a roaring sound.

  The only way to learn to know these sounds is to listen to them repeatedly on the JP training records. Every submarine has these records.

Learn to recognize these other sounds

1. Own ship's screws are heard at 180 degrees, except during silent running.

2. Shrimp snap; porpoise bark and whistle; drumfish sound like a drum; croakers croak.

3. The roaring pound of surf against a beach sounds quite natural.

Illustration of own ship, natural and beach sources of noise.


Contact !

When your searching picks up a suspicious sound, your real job begins. The conning officer needs all the information you can give him. Here is what you must do - and do quickly.

1. Check the reciprocal bearing

Suppose you pick up a contact when the hydrophone is trained on 090 degrees. Immediately train halfway around the bearing circle to 270 degrees. If the sound is weaker here, then you know 090 degrees is the correct contact bearing. But if the sound is stronger on 270 degrees, then 270 degrees is the right bearing to report, because the sound you heard on 090 degrees came through the baffle at the back of the hydrophone.

2. Report the contact

Immediately give the approximate bearing: "JP, contact, bearing ze-ro niner ze-ro." If you are not sure it is a ship, report: "JP, doubtful contact, bearing ze-ro niner ze-ro."

3. Adjust the amplifier controls

While you are reporting, set your amplifier controls to sharpen the target sound:

1. Set volume low enough to make the target distinct from the background noise.

2. Turn filter to the highest setting on which the target can still be heard.

3. As soon as you can hear on the 3000-cycle position, adjust the indicator control so that the magic eye just closes as the hydrophone is swung across the target.

4. Keep reporting accurate bearings

Make your eyes and ears work together. Use both the magic eye and the sound from your headphones to get the best bearings you can. Report every bearing you read. Keep adjusting your volume and filter controls to narrow the arc of the target.

5. Identify the target

As soon as possible, decide the probable kind of target. If it is a ship, notice the speed of the screws (slow, medium, or fast) and the weight of the sound (light or heavy). Report the nature of the target: "JP, bearing two eight eight. Sounds like a destroyer."

6. Keep information going to the conning tower

Get the turn count. Watch for any changes in the speed of the screws or in the loudness of the sound. Report every fact right away.


How to get accurate bearings

Read when sweeping from target's bow through target's stern

To get good bearings and to avoid losing contact, keep crossing the target. Sweep all the way through the screw noise. Then sweep back. Sweep all the way through again and all the way back. Determine which way the target is heading as quickly as possible. Then read the bearing only when sweeping in one direction: from the target's bow through the target's stern. Continue to sweep and to report bearings every time you cross the target in this one direction.

Read the bearing at maximum loudness

As you sweep across the target, the propeller noise increases to maximum loudness, and then dies away. There is also a change in the nature of the sound. Near the bearing of the propellers it has more of a hissing quality. With some experience, you will learn to combine the change in loudness and the change in quality to pick out the maximum point accurately.

If the sound is of equal loudness over a wide arc, proper use of the gain and filters will nearly always narrow it enough to give you a distinct maximum. Also, the more rapidly you sweep, the more noticeable the changes become - and the more accurately you can determine the peak.

Illustration of narrow sweep through arc of sound.
Sweep All The Way Through The Arc Of The Sound.
Report Bearing Where Sound Is Loudest

Use the magic eye

The eye can be brought into operation as soon as you are able to listen on the 3000-cycle filter position. Adjust the indicator control until the eye just closes on each sweep through the target. Read the bearing the instant the eye closes. This should check with the bearing obtained by listening. When ever you change the volume setting, you may have to reset the indicator control.


Use volume and filters wisely

Low volume narrows the target.

As soon as you get a contact, turn the volume control to the lowest setting at which the target can be heard. By cutting down the background noise level, this makes the propeller sounds stand out more clearly. With low volume, the arc of the target noise narrows. This allows you to get more accurate bearings.

Filters can define and narrow the target

Propeller noise is made up of all frequencies. But background noise, from the water and the submarine, is mostly low-frequency sounds. Therefore, by operating with a high-frequency filter you can get rid of the background noise, yet still hear the screws. Also at higher frequencies the target is heard over a narrower arc. So it is wise to use the highest filter setting on which the target can be heard.

Illustration of different filters' effect.
Flat is good position for searching because it permits you to hear all frequencies equally well.
Bass Boost is good for listening to your own ship's noises, which are of low frequency.
500-If a contact is made on FLAT, shift to 500 as soon as you can.  Change the volume if necessary.
3000-Shift to 3000 as soon as the target can be heard on this position. Again change the volume if necessary.
6000 is the best position for reading bearings.  Use it as soon as possible in an approach.


How to take a turn count

1. Train the hydrophone directly on the bearing where the prop beats are loudest.

2. Turn the prop-count detector ON. It may bring out the beats more clearly. (If it does not, turn it OFF.)

3. Notice whether the beats are accented or unaccented. Accented beats go CHUG, chug, chug (three-bladed propeller)-or CHUG, chug, chug, chug (four-bladed propeller). Unaccented beats go chug, chug, chug, chug, chug.

4. Get in rhythm with the beats by pumping your arm up and down. If there is an accented beat, let your hand come down with every accented CHUG -or if the beats are all the same, on every chug.

5. Count the number of times you pump your hand down in 15 seconds.

6. Multiply this count by 4 to get the number of rpm (revolutions per minute). Report the rpm immediately. For example, if your 15-second count is 24, the rpm will be 96, and you will report: "JP, turn count is ze-ro nines six. Good count." If the beats are so rapid that you are not sure of the accuracy of your count, report: "Poor count."

7. After you have reported, make sure that the prop-count detector switch is OFF.

During approach and attack

Give the conning officer every scrap of information you can about the target. Be alert to catch and report:

. . . if it changes its course, turn count, or pinging rate.
. . . if it crosses your own bow or stern.
. . . if another ship comes between you and the target.
. . . if you lose contact.

Listen carefully to all orders from the conning officer. He may direct you to track the target. Or he may tell you to continue searching all around to keep in touch with the escort vessels in the screen, while another sonar operator stays on the target. If he fires torpedoes, he may order you to track them-to give bearings continuously on their whining sound as they run, and to report the crash as they explode.


During evasive maneuvers

In escaping from the enemy, the JP gear is frequently used to keep track of the attacking ship. Because of its topside mounting it can be operated even when you are lying on the bottom. It is also valuable for detecting telltale noises your own machinery may be making, using the bass-boost filter to bring out the low frequencies. If a doubtful sound remains on the same bearing when your own ship changes course, it is almost certainly from your own machinery. You should study our own ship's sounds so that you learn to recognize them quickly.

After depth charges - remagnetize

If depth charges are dropped near you, you probably will have to remagnetize the hydrophone. Plug the cable into the magnetizer jack, and press the push-to-magnetize button just once. Then plug the cable into the hydrophone jack and listen. If you cannot hear anything, magnetize the hydrophone again. Continue this procedure until the hydrophone is able to pick up sounds.

Securing JP gear

As soon as your submarine surfaces, secure the JP gear,

1. Turn the power switch off.

2.Train the hydrophone to 090 degrees if it is installed on the port side, or to 270 degrees if it is on the starboard side.

3. Hang up the headphones carefully. They are a special kind that cannot be replaced while you are on patrol. Other headphones do not work as well on JP gear.

Enemy echo-ranging

If in searching you hear the dull thuds or shrill peeps of enemy pinging (echo-ranging), quickly check the reciprocal bearing, and then report the approximate bearing of the pinging immediately. Estimate the time between pings. If it is over 2 seconds, report "long scale." If it is definitely less than this, report "short scale." Be alert to catch and report any change in the pinging rate.


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Version 1.10, 22 Oct 04