Volume 6, Issue 1 - Naval Sea Systems Command - The US Navy

SEAFRAME
30
Core equities
Sailors assigned to the Ohio-Class fleet ballistic missile submarine USS Pennsylvania
(SSBN 735) spell out the word “Fifty” as they return to Naval Base Kitsap, Navy Region
Northwest . Pennsylvania has just completed its 50th Patrol at sea and a significant
moment in history for the submarine.
U.S. Navy photo.
SIGNATURE DECOMPOSITION (Continued from page 28)
been very useful in advancing, proving, and refining the
technique. It will also be beneficial for future design work
and research and development efforts.”
Nelson Keech, a mechanical engineer, chief
engineer for Carderock Division’s signature analysis
efforts, and a longtime veteran of acoustic investigations,
first introduced the decomposition technique during
the introduction of the USS Seawolf (SSN 21) into the
fleet. “With the quieter signatures,” he says, “we had
to go into a more in-depth analysis to fully quantify
those signatures. The critical thing was development
of high-gain [hydrophone] arrays to generate narrowwidth
“spotbeams,” which basically allowed us to
dissect the signature. That followed on from the Seawolf
to the Virginia Class, and now we’re using it with the
SSGN.” The spotbeams were initially developed as
a quality control tool, but trial personnel realized the
tool could be used to focus on minor components of
a signature. The Performance Assessment community
eventually expanded the use of the tool to bring about
the decomposition analysis.
Mike Marsh, Acting Virginia Class/SSGN
Program Manager, says it has been about a 10-year
process to calibrate and use the beams, and develop the
methods to the point where trial personnel could use the
spotbeams to measure signature levels. “It used to be one
big beam,” he explains, “to make one measurement of the
entire submarine. We broke that down into components
and eventually were able to calibrate those components by
various means. Every year or so, we would do a trial, take
data, learn from it, improve our processes, and do another
trial. Eventually, we arrived at the current methods to do
this kind of analysis.”