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TACTICAL OCEANOGRAPHY SYMPOSIUM INTRODUCTION The United States held a significant anti-submarine warfare (ASW) advantage for decades because of the relative loudness of Soviet submarines. When the Soviets recognized the reasons for the U.S. ASW effectiveness, they applied straightforward, but costly, engineering techniques to submarine design and construction to achieve acoustic quieting. New Soviet submarines, when moving slowly, transmit less sound than their predecessors. It is noteworthy that, despite the Soviet shift to a defensive strategy and their overall reduction of military force, their submarine construction program continues at a pace several times faster than that of the United States. The Soviets are reducing their total submarine inventory by replacing older, noisier submarines with fewer, quieter submarines, with virtually no loss in operational effectiveness. Although the Soviets may now pose less of an offensive threat because of political developments in the Soviet Union, they remain the only viable threat to the U.S. submarine fleet. Threats could be posed by the Soviets and other nations to our submarines, ships, and inland targets. The Soviets have retained a capability to challenge U.S. ASW capabilities, by quieting and increasing the effectiveness of each submarine, and by remaining in home waters (thus depriving the U.S. Navy of opportunities to measure acoustic signatures and practice ASW tactics). A strong fleet of ballistic and cruise missile submarines complement Soviet attack submarine capability. Soviet Arctic capabilities and the proliferation of modern diesel submarines (very quiet, with extended submerged endurance) threaten U.S. freedom of movement worldwide. ASW must therefore remain a high research, development, and operational priority as long as the United States maintains its commitment to guarantee freedom of the seas. il Even under the best conditions, ASW is a complex, lengthy, and equipment- ntensive process. While each ASW unit has unique characteristics, all units rely on acoustics as the primary means of detection, focalization, classification, and, ultimately, attack (using acoustic homing torpedoes). A principal ASW objective is to monitor even the quietest foreign submarines without alerting them, within the greatest geographical range possible. Over the last three decades U.S. systems evolved 1

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toward more precise characterization of acoustic signatures using passive acoustic receivers in very lono arrays. very orecise frequency analysis of received signals, and ~ _ _ _ _ _ _ , _ , , , , , , , , _ long integration times. The principal objective has been to maximize the signal to noise ratio of steacly narrow band signals. Receiver arrays placed on ship hulls, towed arrays, and sonobuoys released from ships or aircraft all shared these characteristics, with optimal band widths ranging from ten to a few hundred Hz. Passive systems were complemented by active systems using frequencies of a few kHz, which were almost exclusively reserved for final localization of the foreign submarines. During this period, use and support of operational systems for environmental science has also evolved. Transmission, reverberation, propagation, and reflection studies have been conducted over much of the northern hemisphere using frequency bands similar to those used by the Na\ry. ASW RESEARCH AND DEVELOPMENT Speakers at the symposium emphasized that the traditional approach described above has been rapidly altered (to the extent permitted by available systems) in the last few years, in response to the changed threat from acoustic quieting. Both operational Navy personnel and system developers have recently concentrated on low frequency passive, low frequency active, and full spectrum detection. ASW research, development, and operations still emphasize acoustics and will continue to do so, given the governing laws of physics. The dramatic change in acoustic signatures of foreign submarines, however, has prompted an interest in monitoring submarines by non-acoustic methods. Academic speakers identified major research and development efforts that have been made in the following areas: characterizing the full spectrum of submarine acoustic emissions, creating a national capability in structural acoustics to help in submarine design as well as analysis of target reflections, understanding the limits of passive long-range detection (centered on the Navy High Gain Initiative), understanding the performance of very loud (220+ db) low frequency active signals, and providing improved environmental predictive and analytical tools and models that help operators understand system performance. 2