The primary goal of antisubmarine warfare is to protect U.S. ships and assets from enemy submarines. Undersea surveillance and detection of submarines are a critical part of this mission. During the Cold War, the Navy relied on a combination of fixed, mobile, passive, and active sonar systems to detect enemy nuclear and diesel submarines, particularly those from the Soviet Union. Passive sonar systems “listen” or receive signals, whereas active systems send out signals to search for targets and receive an echo or response. The systems are used on mobile platforms, such as Navy surface ships, submarines, and aircraft, and in fixed arrays that are laid or buried across the ocean floor in various strategic locations. However, because of technology advancements, the Soviet Union and other countries developed quieter submarines. As a result, submarines became harder to detect, and the Navy grew concerned that enemy submarines could get within effective weapons range of U.S. ships and assets. The Navy determined it needed a system that could detect quiet submarines at great distances. In response to this need, the Navy launched the SURTASS/LFA program in 1985, which was originally designed for use in open oceans. The SURTASS/LFA system operates in conjunction with the Navy’s existing passive SURTASS sonar system. The two components, as illustrated in figure 1, make up a mobile acoustic undersea surveillance system that is intended to provide detection, cueing, localization, and tracking information on modern quiet nuclear and diesel submarines for the battle group or other tactical commanders. The passive component detects sounds or echoes from undersea objects through the use of hydrophones on a receiving array that is towed behind the ship. The active or transmitting component of the system sends high-intensity, low frequency sonar from transducers suspended by a cable under the ship. The active signal will produce a return echo that, when received, provides location and range data on submerged objects. The system uses 18 pairs of undersea transducers and 18 shipboard high-power amplifiers. The SURTASS/LFA system is heavy, weighing 327,000 pounds, and requires a specially designed ship to carry and operate it. The Navy plans to use two SURTASS/LFA systems. The first was installed in 1992 on the research vessel Cory Chouest. The other system, completed in 1993, will be installed on the twin-hull auxiliary general-purpose ocean surveillance ship, T-AGOS-23, which the Navy designed to carry the SURTASS system. The ship was originally scheduled for delivery in 1994, but construction was delayed due to the bankruptcy of the contractor and it will not be completed until late 2002. The Navy estimates that it has cost approximately $375 million to develop and produce the two systems and that it will spend an additional $40 million to field and operate the systems through fiscal year 2009. These estimates do not include the cost of the ships. During the course of developing and testing the SURTASS/LFA system, environmental interest groups, including the Natural Resources Defense Council, began to raise concerns that the system may cause harm to marine mammals. Environmentalists were concerned that the high- intensity sound emitted by the system could cause physical damage to marine mammals and adversely affect their behavior. In August 1995, in a letter to the Secretary of the Navy, the Natural Resources Defense Council questioned whether the Navy had complied with all applicable environmental laws and regulations. In response to growing public concerns and recognition that further assessment of the system was needed, the Navy decided to initiate an environmental impact statement process. As part of this process, the Navy conducted a scientific research program from 1997 to 1998 to test the effects of low frequency sonar on a limited number of whale species off the coasts of California and Hawaii. The Navy distributed a draft environmental impact statement for public comment in 1999 and issued a final environmental impact statement in 2001. The Navy concluded in the environmental impact statement that the potential impact or injury to marine mammals from SURTASS/LFA is negligible. As reflected in the environmental impact statement, this is based on using the system with certain proposed geographic restrictions and monitoring to prevent harm to marine mammals. Because there is some potential for incidental harm to marine mammals, the Navy must obtain a Letter of Authorization from the National Marine Fisheries Service before SURTASS/LFA can be used. The National Marine Fisheries Service issued a draft authorization for public comment in 2001, which concurred with the findings of the Navy’s environmental impact statement. If approved, the authorization would allow the Navy to use the SURTASS/LFA system with certain specified mitigation measures and restrictions. These measures include limiting (1) sonar sound levels to 180 decibels within 12 nautical miles of any coastline or in any designated biologically important offshore area and (2) sound levels to 145 decibels in known recreational or commercial dive sites. In addition, the authorization would require the Navy to monitor marine mammals from the ship visually and with passive and high frequency active sonar. If marine mammals were detected, the Navy would be required to shut down LFA operations to prevent, to the greatest extent possible, marine mammals’ exposure to potentially harmful sound levels. The decision on the authorization is expected later in 2002. Notwithstanding the mitigation measures outlined by the Letter of Authorization, environmental organizations are still expected to oppose the use of the SURTASS/LFA. They have indicated that although conclusive evidence has not been established regarding the harmful effects of the SURTASS/LFA on marine mammals, enough is known about the potential adverse effects of sound on marine mammals to warrant no further use of the system. They have also questioned the usefulness of the system to the Navy. The Navy has also recognized gaps exist in scientific knowledge about the impact of the system on marine mammals, but it considers that the risk is minimal and not enough to warrant ceasing its use. In addition, the Navy has stated that it has done an extensive amount of testing, research, and analysis regarding the use of SURTASS/LFA and marine mammals and that current information combined with the planned mitigation and monitoring procedures and ongoing research, support resuming SURTASS/LFA operations. Furthermore, the Navy has emphasized that the need for a long-range detection capability still exists. Based on initial testing conducted to date, SURTASS/LFA appears to provide long-range undersea detection capabilities in the deep, open ocean that surpass any system planned or in existence. However, the system may not be as effective in littoral waters. A final operational evaluation must still be conducted to determine the overall effectiveness and suitability of the system, and while Navy officials are developing a plan to evaluate the system, they have not yet defined what testing will be conducted in littoral areas. The primary benefit of SURTASS/LFA is that it will provide a significant increase in long-range undersea detection capability in the open ocean. Active sonar at low frequencies is more effective and transmits further undersea because its absorption rate in water is relatively low. Because of this, a low frequency active signal can travel several hundreds of miles if unimpeded. In contrast, mid frequency and high frequency sonar transmits on the order of tens of miles. Therefore, low frequency active sonar can potentially cover an area of the ocean vastly greater than sonar at higher frequencies. In addition, a benefit of active sonar is its ability to seek out targets rather than wait passively for a target to approach. As a result, a system such as SURTASS/LFA can provide the means to detect enemy submarines before they can get within the effective weapons range of U.S. ships. Also, because it is mobile, the system provides greater deployment flexibility and can detect target information in areas beyond the reach of fixed sonar systems according to Navy officials. Moreover, the SURTASS/LFA technology can provide long-range detection with less assets and operators than other technologies. SURTASS/LFA also has several operational limitations, including the amount of coverage it can provide and its vulnerabilities. The Navy plans to use a total of only two systems, with one deployed to the Pacific Fleet and the other to the Atlantic Fleet to support antisubmarine missions. Therefore, the amount of area the system can cover will be limited. The Navy recognizes that two systems are not sufficient to meet operational requirements and prefers to have more. In addition, SURTASS/LFA may be vulnerable to attack because the ships carrying the systems will not have onboard defense systems. The ships are also relatively slow and therefore incapable of remaining close enough to the transiting battlegroup to be protected. Furthermore, because SURTASS/LFA transmits an active, high volume signal, it can readily reveal its location, which further increases its vulnerability. However, the Navy concluded that the operational limitations are outweighed by the benefit of long-range detection. Results of SURTASS/LFA testing to date show that the system will increase the Navy’s capability to detect modern submarines at long range in deep, open ocean areas. Starting in 1989 through 1992, the Navy conducted a series of developmental tests on SURTASS/LFA that were focused on validating the performance of a demonstration system in these areas. The objectives of these tests were to obtain an increased understanding of technical performance issues such as the long-range transmission of signals and signal processing techniques. Based on the successful results of these tests, the Navy concluded the system performance requirements were achievable and decided to proceed with full-scale engineering development. In 1992, the Navy began conducting operational tests using an engineering development model that more closely represented the operational SURTASS/LFA system. The purpose of these tests was to determine the performance of the system under more realistic at-sea conditions and against more realistic threat scenarios, including quiet submarines.