Project Artemis

Project Artemis was a project undertaken by the United States Navy in the 1960s, which produced a low-frequency active sonar system that could detect submarines at long range. Robert A. Frosch, in his capacity as Technical Director of Hudson Laboratories (Columbia University), was technical director of the project. Dr. Frosch later went on to be the 5th administrator of NASA. The project was named in honor of Frederick Vinton Hunt. Since Artemis is the goddess of the hunt, the name of the project is in deference to F. V. Hunt who proposed the idea in 1951.

Ship modifications
The active array was deployed from a ship, but only as a platform of convenience, since a permanent installation in deep water was extremely costly. The ship's purpose was station-keeping and the ability to orient itself. A World War II tanker, USNS Mission Capistrano was modified to carry the ultra‑high‑powered sonar transducer array. Upon completion of her conversion, she joined Project “Artemis”.

A 500-shaft horsepower, controllable-pitch screw propeller was installed in a transverse tunnel through the forefoot of the USNS Mission Capistrano. The propeller, commonly called a bow thruster, delivered 11,250 pounds of thrust during dock trials. Its use was for the single purpose of controlling the vessel's heading when lying to in the open ocean. Under these conditions, it is reported capable of swinging the ship to any given bearing and maintaining it to within one degree of yaw in sea conditions of 15 knot winds and five foot waves upon six foot swells.

Active array specifications
The active portion of the Artemis array was 50 ft by 33 ft and weighed 400 tons. It consisted of 1440 individual transducers (200 pounds apiece) in a 48 by 30 configuration. The array was developed by Massa Products in Quincy, Massachusetts. The frequency range was 350 to 450 Hz, with a source level of 247 dBm (units? reference 0dB=?) and an acoustic power of 1 megawatt. The transducer could be raised and lowered like a centerboard through the ship’s bottom. The transducers could be deployed to a depth of 1200 ft. The system was not meant to be mobile, and was only used when the ship was in station-keeping mode.

Receive system and monitoring
The passive receive array consisted of ten strings of hydrophones mounted on 200 eighty-foot towers laid down the side of Plantagenet Bank in Bermuda. The strings were laid on the side of the bank using the U.S. Navy large covered lighter YFNB-12, reconfigured with a long overhead boom to handle the towers. Each cable had special takeouts built into it at intervals from which wires to the hydrophones were connected. Each tower was clamped onto the special cable with takeouts. At the upper end of the approximately 4 in cable a wire rope was attached and led to an explosively embedded anchor shot into the flat coral top of Plantagenet Bank. Tension of more than 40,000 lb was applied to the wire rope and cable to lay it down the side of the bank in the straightest line possible. At one point all further construction ceased while a stopper was placed on the special cable because most of the connection to the wire rope had broken and the string was being held by a few strands of wire on the double drum winch on YFNB-12. The YFNB-12 was held in place with four Murray and Tregurtha Diesel outboard engines placed on the corners and capable of 360 degree rotation, developing tremendous thrust in any direction. The cables led to Argus Island tower, from which the signal was conducted to the United States listening post located at Tudor Hill, Southampton, Bermuda (32.26412°N, -64.87767°W) that had opened on June 1, 1955. At the time the post was classified top secret. Tudor Hill Naval Facility Bermuda was closed in 1995. The facility shares a short road with the Pompano Beach Club.

Part of the Artemis system was Argus Island, located at 31.9498°N, -65.1775°W, an oceanographic research tower, which had been erected in 1961 by the United States Navy on Argus Bank 35 mi southwest of Bermuda in 192 ft of water. After eight years of use, the tower was condemned as unsafe in 1970 and was demolished in 1976, removing a major navigation aid for sport fisherman.

Feasibility of permanent installation
A feasibility study for developing the amplifier transducer and energy storage system to be associated with a nuclear-powered, remote, unattended high-power acoustic source was investigated. The results of this study indicated that such a system was feasible. No system of this type was ever procured. The use of fixed low-frequency systems was abandoned in the mid-1960s, and replaced with mobile systems like the one on USNS Impeccable (T-AGOS-23).

Political context
In 1959 the Soviet Union was deploying its first generation Intercontinental Ballistic Missiles, R-7 Semyorka. They were capable of delivering its payload at around 8,800 km, with an accuracy (CEP) of around 5 km. A single nuclear warhead was carried with a nominal yield of 3 megatons of TNT. However, they were very new and turned out to be very unreliable.

K-19, the first nuclear-powered Russian boat, was commissioned on 30 April 1961. The military at that time considered the single greatest security threat to the USA the possibility of a submarine-delivered nuclear warhead placed near a major American city. Artemis was considered part of an underwater Defense Early Warning system. However, it was discovered that the Soviet boats were particularly noisy. Rapid advances in computer technology and the development of signal processing algorithms, such as the Fast Fourier transform, quickly gave the West the superior military position using multiple passive SOSUS arrays. In 1961, SOSUS tracked USS George Washington from the United States to the United Kingdom. The next year SOSUS detected and tracked the first Soviet Diesel submarine.

The Artemis active systems were eventually retired, since the passive systems proved adequate to detecting submarines that threatened the American coast. Largely because of the spy ring operated by John Anthony Walker in 1968, and the development of the submarine-launched intercontinental ballistic missiles, the need to send ballistic submarines directly to the American coast diminished. The Soviet Union began to rely more on a Bastion, whereby the latest generation of SSBN was deployed only in well-protected nearby waters. A mobile surveillance capability, called SURTASS, was developed in the mid-1970s. This system passed Operational Evaluation (OPEVAL) in 1980 and the ships began to be deployed. By 1985 Soviet naval exercises in the North Sea were using as many as a 100 vessels, including attack submarines. Chief of Naval Operations enacted the Urgent Anti-Submarine Research Program (CUARP), whose centerpiece was to activate the SURTASS fleet with a low-frequency system, and to develop tactics for such a system. The mobile system was considerably smaller than the Artemis transducer array, weighing roughly one-sixth as much.

With the diminished threat of the Atlantic SSBN, the Surveillance Towed Array Sensor System was redeployed in the Pacific where a new generations of Attack submarines and Ballistic missile submarines were being deployed by several countries. The low frequency active system is currently being deployed on the USNS Impeccable.