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	Director, Operational Test & Evaluation
FY97 Annual Report

SURVEILLANCE TOWED ARRAY SENSOR SYSTEM (SURTASS)

	Navy ACAT II Program 24 systems Total program cost (TY$) $1495.9M Average unit cost (TY$) $60.5M Full-rate production 4QFY00 Prime Contractor Halter Marine Inc.

SYSTEM DESCRIPTION & CONTRIBUTION TO JOINT VISION 2010

SURTASS is an element of the Integrated Undersea Surveillance System, providing mobile detection, tracking, and reporting of submarine contacts at long range, thereby contributing to the operational concepts of full-dimensional protection through information superiority. The current, or baseline, sensor is a long array of hydrophones towed by a dedicated non-combatant ship designated T-AGOS. There are two upgrades. The Block Upgrade improves the passive-only sensor with advancements against quiet threats including improved sensitivity and signal processing and use of a reduced diameter hydrophone array. The Low Frequency Active (LFA) upgrade is a long-range active sonar designed to detect even quieter threats in the future. The LFA system includes a large source array for active transmissions and the array of the Block Upgrade as a separate receiver. In its final configuration, SURTASS LFA will include the Block Upgrade and can be used either as a passive system or in one of two active modes of LFA: monostatic or bistatic receive.

Four inter-related programs encompass the SURTASS systems: the T-AGOS 19 and T-AGOS SURTASS NAVY 23 class shipbuilding programs and the SURTASS Block Upgrade and LFA programs. Existing baseline SURTASS suites on monohull-hull T-AGOS ships are being deactivated and T-AGOS 19 and 23 class vessels will replace them. The new vessels feature a small water-plane area twin hull (SWATH) design which provides quieting to enhance performance of the reduced diameter array and greater stability in high sea states for the LFA source array. T-AGOS 23 class ships are larger than T-AGOS 19 ships in order to handle the larger and heavier equipment for the LFA system. Original procurement was projected for up to five T-AGOS 23 class ships; the current program is in flux, but will certainly be more modest. The SURTASS Block Upgrade will back-fit into T-AGOS 19 (currently with a baseline system) and will be the sensor suite (passive receive only) for T-AGOS 20 through 22. Eventually T-AGOS 19 through 22 will also have a capability to receive and process bistatic LFA signals.

IOT&E was completed in October 1992 in the Gulf of Alaska, testing an engineering develop-ment model (EDM) of the LFA system installed in a converted, monohull research vessel. The SURTASS LFA system was found to be potentially operationally effective and potentially operationally suitable.

In May 1992, DOT&E approved a test plan for OT-IIA of the T-AGOS 19 SWATH platform to assess its ability to support SURTASS operations in two phases: one to evaluate equipment operation and seakeeping in heavy weather, and a second phase to compare acoustic performance to an exist monohull T-AGOS vessel. The first phase, conducted in the North Pacific in up to sea state 7 (wave heights to 30 feet) was completed in October 1992. The second phase, conducted north of the Hawaiian Islands in May/June 1993, included a SWATH and a monohull T-AGOS vessel, operating against a towed projector serving as an acoustic target. For both phases of testing, the vessels were outfitted with the SURTASS Baseline System, which allowed a determination of system survivability in high sea states in Phase I, and a thorough comparison of detection and localization/tracking effectiveness in Phase II.

Composite results of both phases found that the T-AGOS 19 SWATH platform was operationally effective and operationally suitable to support the SURTASS Baseline System. The platform was found to be potentially operationally effective and potentially operationally suitable to support the SURTASS Block Upgrade system, yet to be installed. The Block Upgrade systems were subsequently installed aboard the SWATH T-AGOS ships and proceeded through development testing.

The SURTASS Block Upgrade OPEVAL (OT-IID) was conducted over a 7-day period in November 1994 in the North Atlantic Ocean. The OPEVAL utilized the USNS ABLE (T-AGOS 20) as the SURTASS sensor and the detections of the target were made at the Naval Ocean Processing Facility at Dam Neck, VA. Of primary concern were the four unresolved issues from OT-IIB. They were: Acoustic Performance Prediction, Logistic Support-ability, Training, and Documentation. The USS SCRANTON (SSN 756) simulated a threat target. Sea states during the test ranged between sea state 3 and sea state 7. The test also included intentional bow thruster operations to determine the impact upon detection in order to resolve a prior deficiency.

In OT-IID, SURTASS performed in accordance with the TEMP, was tested in high sea states, an important goal in the SWATH T-AGOS and Block Upgrade programs, and demonstrated minimal interference from the bow thrusters. Furthermore, the issues of Acoustic Performance Prediction, Logistic Supportability, Training, and Documentation, were resolved satisfactorily. The Block Upgrade successfully met all sonar detection Figure of Merit requirements. Localization and tracking accuracies were satisfactory. While there were some deficiencies, the Navy found the Block Upgrade System to be operationally effective and suitable.

In June 1996, SURTASS LFA participated in a major fleet exercise, RIMPAC 96, including the preparatory exercise, TEAMWORK NORTH. The LFA, installed aboard the R/V Cory Chouest operated with a U.S. battle group together with the ships of five allied Pacific nations in open ocean south of the Hawaiian Islands. In conjunction with the exercise, COMOPTEVFOR conducted an OA (OT-IIE) to evaluate the use of Cory Chouest as an interim fleet asset pending the completion of the SWATH ship T-23.

No operational testing field activity was scheduled or conducted in FY97. However, data analysis of RIMPAC 96 continued and confirmed the significant potential that these exercises have for realistic operational testing. The current TEMP is being complied with.

In TEAMWORK NORTH the LFA system detected a foreign submarine while making a transit to the Hawaiian Island area. In RIMPAC 96, LFA performed effectively by detecting all designated exercise participants. Environmental impact of LFA has recently become an issue and data is now being collected to support an environmental impact statement for the RIMPAC 98 exercise. There is growing concern that testing of all active acoustic detection devices in shallow water ranges may be at risk due to environmental considerations.

The test pointed out the need for further tactics development and the need to concentrate on fleet integration issues. In addition, there were software reliability problems. In spite of these shortcomings, Cory Chouest was approved as an interim fleet asset and will continue to operate with the Pacific Fleet with a view toward RIMPAC 98, when another Operational Assessment (OT-IIF) will be done.