As analyzed in the 2001 EIS, the only technology (acoustic or
non-acoustic) capable of providing reliable, long-range
detection of today’s quieter, harder-to-find submarines is low
frequency active sonar. The Navy has developed other passive
sonar technologies, such as Advanced Deployable System (ADS) and
Twin Line SURTASS, but even with these upgrades, passive sonar
systems are not sufficient to meet the needed long-range
detection that only LFA sonar can provide.
When the Navy is attempting to locate submarines, the priority
is to detect the target passively at distances far enough away
so that the submarine is outside of its effective weapons range.
When a ship uses active sonar, the active “ping” gives away the
ship’s position, which can be lethal if an enemy submarine is
lurking within its weapon’s range when it hears the ping. So,
the Navy will only use active sonar when passive alone will not
meet its needs. This can occur when the acoustic “signature” of
the target cannot be heard over the din of the surrounding noise
in the ocean. In this circumstance, the use of active sonar is
the only viable alternative.