The AN/BQR-15 is a passive towed array sonar system used by the U.S. Navy on submarines. It was the first towed array designed specifically for ballistic missile submarines (SSBNs) and was initially installed on the Ethan Allen class (SSBN 608), Lafayette class (SSBN 616), James Madison Class (SSBN-627) and Benjamin Franklin class (SSBN 640).
Over time, the system was also adopted for attack submarines, including the Los Angeles class (SSN 688) and the most modern ballistic submarines of the Ohio class (SSBN 726).
Incorporating the AN/BQR-23 Towed-Array processor, the BQR-15 significantly improved passive detection and classification capabilities. It enabled submarines to detect and classify potential threats from a distance while maintaining a covert posture.
This technology provided submarines with long-range detection, the ability to monitor self-noise, and the capability to receive underwater communication signals, all while minimizing the risk of detection.
Description
The BQR-15 towed array sonar system consists of four main components: beamformer equipment, handling equipment, the towed array assembly, and display equipment. The towed array itself is responsible for receiving acoustic signals from targets and transmitting them to the sonar display.
The AN/BQR-15 HF sonar system includes a 670-meter cable (2,200-foot) and a 47-meter-long (156 feet), 9 cm diameter array that houses 42 hydrophones. This passive array is towed by the cable that is deployed from the submarine.
The system is capable of forming 46 beams on fixed bearings, with an additional two steerable analog beams covering any of 23 bearings. It can also form beams directed to any of 92 bearings. This advanced beamforming technology reduces interference from the submarine’s own noise, except in a few forward sectors.
The array’s non-rigid construction and slender form ensure low self-noise, enhancing passive detection capabilities. Under ideal conditions, the array can be deployed in as little as 15 minutes.
Development history
Early studies
The development of the BQR-15 towed array sonar began in response to U.S. Navy SSBN commanders’ demands for improved stern protection and enhanced target classification. By 1965, the Navy had initiated feasibility studies for a towed array system for both ballistic missile submarines (SSBNs) and attack submarines (SSNs). At the time, the Navy had already experimented with towed arrays on surface ships, but the technology was not yet mature enough for widespread adoption.
Trials on the USS John Marshall (SSBN 611) demonstrated that when the analyzer was switched to the towed array, unwanted noise from the submarine disappeared, providing clearer acoustic data. These findings led to the Navy’s decision to adopt the SSBN array as the BQR-15.
The BQR-15 employed a beam-former that fed a frequency analyzer, allowing submarines to classify targets from all bearings except directly ahead while providing superior stern coverage. This array could also minimize interference from the submarine’s own machinery, a critical advantage over traditional hull-mounted sonar systems that suffered from significant self-noise at low frequencies.
Procurement and Deployment
Development of the BQR-15 was completed in fiscal year 1972 at a cost of approximately $20 million. The main contractor was Western Electric Company, Inc., a subsidiary of AT&T. The initial program called for the procurement of 26 systems for Fleet Ballistic Missile (FBM) submarines, as well as spare parts and training equipment for FBM facilities in New London, Charleston, and Pearl Harbor.
By May 1974, four BQR-15 systems had been delivered, with the first installations on USS Mariano G. Vallejo (SSBN-658), Sam Houston (SSBN 609), USS Thomas A. Edison (SSBN 610), and USS Will Rogers (SSBN-659. Additional systems were procured under the fiscal year 1975 budget for SSBNs USS Ethan Allen (SSBN 608), USS Tecumseh (SSBN 628), USS John C. Calhoun (SSBN 630), USS Ulysses S. Grant (SSBN 631), USS Von Steuben (SSBN 632), and USS Francis Scott Key (SSBN 657).
By fiscal year 1976, a request for $16.6 million aimed to complete the procurement of the 26 required systems, along with additional units for FBM training sites.
SPAD and AN/BQR-23
In May 1972, contracts were awarded for developing the Signal Processing and Display (SPAD) systems to exploit the capabilities of the BQR-15 array fully. However, due to delays and technical difficulties, this effort was canceled in March 1974, and funds were reallocated for multiple-channel signal processing equipment.
The first AN/BQR-23 contract, specifically designed as a towed array processor for use with the BQR-15, was awarded in 1974. The AN/BQR-23 supported at least 64 simultaneous LOFAR channels in real-time and featured bearing-interpolation trackers to smooth data. It provided both LOFAR and frequency-azimuth display formats for the BQR-15 sonar system.
AN/BQR-15 SPALT 9080
As part of the Strategic Projects Alterations (SPALTs), several modifications were made to the AN/BQR-15 sonar system for deployment on the new Ohio-class Trident submarines.
A significant enhancement was the introduction of the 9080 thin-line towed array. This new generation of digital towed sonar arrays was developed to provide high-resolution target detection at greater ranges and higher towing speeds.
The 9080 thin-line towed array has an outside diameter of just one inch. Despite its slender profile, it features a wide acoustic aperture and low self-noise, ensuring reliable performance in various underwater conditions. The array’s acoustic channels are digitized and multiplexed onto a coaxial signal path leading to inboard signal processing equipment.
Sophisticated digital signal processing is integral to the 9080 array. Unlike earlier systems, the 9080 array utilizes the Rockwell AN/BQQ-9 Towed-Array Signal Processing Equipment (TASPE) instead of the AN/BQR-23 processor.
Contractor
Western Electric Company, Burlington, North Carolina, USA.
Specifications
| Specification | Details |
|---|---|
| Towed Array Length | 47 meters (156 feet) |
| Towed Array Diameter | 9 centimeters (3.5 in) |
| Number of Hydrophones | 42 |
| Towed Cable Length | 670 meters (2,200 feet) |
| Beamforming Capabilities | - Forms 46 beams on fixed bearings - 2 steerable analog beams covering any of 23 bearings - Can form beams directed to any of 92 bearings |
| Deployment Time | Can be deployed in as little as 15 minutes under ideal conditions |
Further reading
- United States Nuclear Ballistic Missile Submarines (SSBN)
- Ethan Allen-Class (SSBN-608) Ballistic Missile Submarines
- Lafayette-Class (SSBN-616) Ballistic Missile Submarines
- James Madison-Class (SSBN-627) Ballistic Missile Submarines
- Benjamin Franklin-Class (SSBN-640) Ballistic Missile Submarines
- Ohio-Class (SSBN-726) Ballistic Missile Submarines
- AN/BQR-23 Towed-Array Processor
Bibliography
- Jane’s Weapon Systems. (1978). United Kingdom
- Jane’s Weapon Systems. (1985). United Kingdom: F. Watts.
- Friedman, N. (1989). The Naval Institute guide to world naval weapons systems. Annapolis: Naval Institute Press.
- Research, development, test, and evaluation. (1974). United States: U.S. Government Printing Office.
- Friedman, N. (2020). British Submarines in the Cold War Era. United Kingdom: Pen & Sword Books.
