Listening sonobuoy AN/SSQ-2  is expendable equipment used to detect underwater sounds and transmit them by radio to nearby aircraft or to other stations equipped with a suitable receiver. It is designed to be carried and launched from naval aircraft, particularily from carrier and patrol aircraft and dropped under the following  conditions:

a) at a  speed of not more than 150 knots when at a minimum altitude of 150 feet or
b) at higher speeds up to 250 knots at a minimum altitude of 500 feet.

Upon being dropped from the aircraft, four blades on the cap of the sonobuoy open and rotate to stabilize and slow its descent to the water. Upon impact with the water, the rotating blade assembly is jettisoned, the dye-marker tubes are broken and a red dye colours the surrounding water. Next, the hydrophone is released and submerges to the end of its 40 foot cable. The FM radio antenna is ereccted and sea water enters the A-battery compartment. The sea water activates the A-battery and within a minute, the equipment is in operation.

Underwater sounds detected by the hydrophone are amplified and frequency rnodulate the transmitter. When signals from this transmitter are received and demodulated in a suitable receiver, they provide a means of identifying and locating the underwater sound source.

Location of the sonobuoy while in operation is revealed at close range by the red dye-marker in daylight and by two incandecent lamps at night. For locating  the SSQ-2 at greater distances there is a beacon receiver having an
antenna which receives X and S band radar signals. The beacon receiver triggers a blocking oscillator, which in turn, amplitude-modulates the final stage of the transmitter. These reply signals can be detected for approximately  15 miles on the S radar band or 10 miles on the X band.

The unit incorporares an automatic scuttling device consisting of a water soluble plug in the casing below the water line. When this plug dissolves, the interior of the equipment is flooded, causing it to sink. The floating period is a function of the water temperature, with the plug dissolving more rapidly in warmer water. If recovery is desired, the plug can be covered with tape before the equipment is launched.

AN/SSQ-2. (Image courtesy HNSA)

Power Supply: Battery operated from a special dry B-battery and a sea water activated A-battery. The B- battery supplies 150, 45, -3 and -15 volt outputs. The A-battery provides 1.2 and 2.5 volt outputs. The no-load voltage of the B-battery is around 180 volts.

Transmitter Power Output: At least 0.25 watts

Frequency Range: Each unit is adjusted to one of the assigned carrier frequency channels within the l62 to 174 MHz range. The channel number is stencilled near the base of the case.

Beacon Range:

X-Band - 10 miles, smooth sea and aircraft at 2,000 feet.
S-Band -  15 miles, smooth sea and aircraft at 2,000 feet

Beacon Range Error: Not in excees of 600 yards (for triggering signals of 1 microvolt or greater.

Beacon Azimuth Error: AGC prevents triggering by minor lobes of interrogating radar.

Beacon Antenna Pattern: Omni-directlonal in a horizontal plane. 60  to 70 degree vertical beam with maximum near horizon.

Hydrophone Depth: Maximum 40 feet.

Hydrophone Listening Range: One half to 4 miles as determined by ambient water noise undersea conditions

Operating Life: At least 1.5 hours in sea water at 0 to 30C

Shelf Life:

Equipment: 5 years
Battery: 1 year at minimum temperature of -35C or maximum temp of 22 C

Circa: November 1951

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Credits and References:

1)   SSQ-2
2)   Bert Campbell,  Argus Navigator <navigator1(at)>

March 21/09