VOLUME I Multinational Maritime Tactical Instructions and Procedures

MTP 1(D), Vol. I
SECTION V — EMPLOYMENT OF ELECTRONIC AND ACOUSTIC SUPPORT
MEASURES (ESM/AWSM)
5500 INTERCEPTION, DETECTION, AND DIRECTION FINDING (DF) OF TRANSMISSIONS
a. The objective of ESM/AWSM search is to provide the tactical advantage of “first sighting” by
passive means. The first indication of an enemy’s presence may be provided by interception of his
emissions. In addition, early interception allows the timely preparation of countermeasures.
b. In order to conduct ESM/AWSM search for an enemy, complete and continuous coverage of the
frequency spectrum is required together with as wide a geographic dispersion of intercept equipment as
possible.
c. Intelligence sources may provide information on the frequencies emitted by the enemy and, in
certain cases, give actual frequencies used, or likely to be used. It is, therefore, possible for the OTC/CWC
to organize ESM/AWSM search to cover specific frequencies.
5510 ELECTROMAGNETIC INTERFERENCE (EMI) OF SEARCH EQUIPMENT BY OWN
TRANSMISSIONS
a. Interference caused by radiations from electronic transmitters of ships in company may reduce
the effectiveness of passive sensors. Radars, in particular, by reason of their short pulses at peak power,
produce powerful harmonics that can make reception in a sensitive search receiver difficult in adjacent
bands, and almost impossible in the same band. It is possible to reduce this interference by using a very
narrow bandwidth, a filter, or a suppression device in the receiver. This may result in a corresponding loss
of intercept probability.
b. Interference may also be caused by accidental radiations, such as sparking in motors or
generators, or by lack of electromagnetic compatibility (EMC).
5511 ACOUSTIC INTERFERENCE OF SEARCH EQUIPMENT BY OWN TRANSMISSIONS
a. Interference caused either by own ship’s radiated noise or by active sonar transmissions can
reduce the effectiveness of sonar receivers both in own ship and other units in a force.
(1) Own ship’s radiated noise is sound that is inadvertently transmitted into the water, predominantly
by machinery, cavitation from propellers, ship’s movement, and flow noise. These can be exacerbated
by manmade noises caused by unsecured equipment and electrical/electronic circuits in the ship.
Radiated noise can be reduced but not eliminated by good husbandry of machinery, propellers, and general
securing of equipment throughout the ship.
(2) Sonar transmissions can cause mutual interference with other units operating in the same vicinity,
particularly when two frequencies are close. This can be received directly or through reverberations
that increase background noise. Interference can be reduced by placing units with similar sonar frequencies
on opposite sides of the screen.
b. Passive sonar can be confused by high acoustic levels; for example, units in a departure screen
streaming noisemakers/operating echo sounders/transmitting on UWT could mask the acoustic signature
of a heavy unit passing through the area from a listening submarine.
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