Project Artemis

Project Artemis was a United States Navy acoustics research and development experiment from the late 1950s into the mid 1960s to test a potential low-frequency active sonar system for ocean surveillance. The at sea testing began in 1960 after research and development in the late 1950s. The project's test requirement was to prove detection of a submerged submarine at. The experiment, covering a number of years, involved a large active element and a massive receiver array.
The receiving array was a field of modules forming a three dimensional array laid from 1961 to 1963 on the slopes of a seamount, the Plantagenet Bank, off Bermuda. The modules, attached to ten lines of cable, were masts with floats on top to keep them upright. Each module mounted sets of hydrophones. The receiving array terminated at Argus Island, built on the seamount's top, with data processed at the laboratory that was also constructed for the project. The laboratory was then the Bermuda Research Detachment of the Navy Underwater Sound Laboratory.
The active source array was to be suspended at to from the former tanker. The 1440-element active array had a one megawatt acoustic output with a center frequency of 400 Hz.
Though Artemis failed the final test and resulted in no operational system, it set the agenda for research in ocean acoustics and engineering such systems for the future.

Background

World War II experience prompted the U.S. Navy to examine the threat of Soviet submarines which had been improved by captured German technology. As a result of the threat being considered high risk sonic detection became a top priority. The Navy approached the National Science Foundation's Committee for Undersea Warfare for advice. Following the recommendations the Navy established a study under Massachusetts Institute of Technology auspices designated Project Hartwell which in 1950 recommended development of a long range passive acoustic detection system. By 13 November 1950 a letter contract had been issued to Western Electric to develop the bottom array system exploiting low frequencies. A test array was laid in the Bahamas off Eleuthera and upon successful tests with a U.S. submarine an order for six such systems was issued in 1952. The Sound Surveillance System, its name and purpose classified, was given the unclassified name Project Caesar to cover its development and maintenance. In 1956, as the last of the Atlantic SOSUS systems were being installed, Chief of Naval Operations Admiral Arleigh Burke convened a summer study similar to the Hartwell study designated the Nobska Study coordinated by the Committee on Undersea Warfare. Admiral Burke was particularly concerned with the threat of Soviet nuclear submarines in light of the capabilities of the nuclear submarine had been demonstrated.
Much of the study focused on undersea warfare and the need for nuclear anti-submarine submarines but also, in looking at SOSUS, recommended research and development of potential long range, active sonar systems. It also focused on the need to understand the ocean environment. A particular area of investigation was whether an active system could be developed with the power and directivity to exploit ocean zones the passive system being installed might not. With respect to the Navy active sonar project designated Artemis, to run from 1958 to 1963, an understanding of the ocean environment was vital. If the project was to succeed the full efforts of every ocean scientist, technician and laboratory on the Atlantic coast was likely required yet there were only six to seven hundred such people that were qualified. The need to meet that requirement and long term antisubmarine needs of the Navy drove large increases in academic and research budgets for oceanography.
As Project Artemis was undergoing tests in the early 1960s SOSUS tracked the first U.S. ballistic missile submarine across the Atlantic in 1961. In June 1962 SOSUS made the first detection and classification of a Soviet diesel submarine, and during the Cuban Missile Crisis in October tracked Soviet Foxtrot-class submarine with correlated sighting by aircraft. On 6 July 1962 the SOSUS array terminating at Barbados demonstrated detection range by identifying a Soviet nuclear submarine transiting off Norway.

Project overview

A commercial contractor had proposed a long range, active sonar surveillance system to the Navy but a review by Hudson Laboratories showed there were flaws in the basic numbers upon which the proposal looked feasible. Frederick V. Hunt of Harvard had proposed that a goal should be a scan of "an ocean an hour" that was based on the sound speed in seawater so that 3600 seconds equals 3600 miles so that round trip travel time would allow surveillance of an entire ocean from mid ocean. Though the consensus was that contractor's proposed system would not work as conceived there were possibilities something in the field of active sonar could work to meet Hunt's concept. Artemis, Greek goddess of the hunt, was given to the project as a name for that relationship, making it unusual in not being a code word or acronym. Project Artemis experimental and system development effort's goal was to define requirements for a long range, low frequency, active, sonar capable of detecting a submerged submarine at about. The concept was a possible undersea equivalent of the Arctic Distant Early Warning radar system. A secondary objective was to define the techniques and problems in fixing such arrays in fixed bottom locations for an operational system.
Artemis involved nearly the entire national acoustics community at the time. A Bell Telephone Laboratories representative initially reviewed plans with a research committee established to continue review of plans and progress. Hudson Laboratories, directed by Dr. Robert Frosch, had been established by the Office of Naval Research to balance Navy laboratories with interests in systems. Hudson Laboratories was the prime contractor for the project with Dr. Frosch as Chief Scientist of Project Artemis. He was followed by Dr. Alan Berman, the laboratory's Associate Director, as Hudson's Director and Chief Scientist of Project Artemis. The Artemis Research Committee chaired by BTL included members from the Marine Physical Laboratory of Scripps Institution of Oceanography, Naval Ocean Systems Center, both based in San Diego, Naval Underwater Systems Center, Naval Research Laboratory, Hudson Labs, IBM and others oversaw and coordinated technical matters. Contractors ranged from Western Electric and General Electric companies to small study contracts to General Atronics Corporation.
The acoustic propagation paths as understood at the time, operating depths of submarines and ray tracing for sound velocity conditions as understood in the Atlantic determined that the sound source depth should be at to with a center frequency of 400 Hz. The transmitting array deployment evolved from a fixed bottom site, a deployment from an anchored or tethered ship with the final decision that it was to be deployed by the converted tanker Mission Capistrano which would be equipped with station keeping capability.
The 10,000 element, three dimensional, receiver array was composed of elements laid in a field as 210 modular masts in ten strings with an additional horizontal line on the slopes of Plantagenet Bank off Bermuda between 1961 and 1963. The Bermuda Research Detachment was established with a building on Tudor Hill adjacent to Naval Facility Bermuda and the Argus Island offshore tower was built for termination of Artemis receiver cables.
A test was made, after several years of development, with a submarine at the design range of 1,000 km and fitted with a transponder reacting to the active array's signal for reference. The Artemis system failed the test. Station keeping issues of the active array ship, degradation of the receiving system modules and poorly understood ocean acoustics were involved in the failure.
No operational system resulted from the effort but it defined the limitations of technology and understanding of underwater acoustics of the time. In particular understanding of scattering and reverberation was shown to be lacking. The Artemis receiving array was expected to demonstrate problems with multipath reflections but experienced considerable failure with floats upon which its configuration relied. Surveys by the submersible Alvin in 1966 and 1967 found multiple float failures with collapsed modules and other damage to standing modules.
The major technological limitation was found to be computing capability, particularly speed, that forced use of analog devices for beam steering and signal processing. Results in acoustics formed the basis for extensive ocean acoustics research going forward after the project's termination in the mid 1960s. The project successfully proved techniques for developing and deploying high powered, phased active hydrophone arrays.

Passive receiving array

The receiving array, just as with the source, underwent significant changes from planning to the final test configuration. It was a three dimensional system of hydrophones laid by cable ships on the slope of the Plantagnet Bank seamount. The array cables terminated at Argus Island, the tower erected for the project on the bank. The tower passed the data to the laboratory built and staffed for the project at Tudor Hill, Bermuda.

Undersea array

The passive receive array field consisted of ten parallel cables with 210 modules composed of masts mounting hydrophones. The cables were laid down the slope of Plantagenet Bank in Bermuda. A 1961 array was to the north east of and parallel to array field string number one and a horizontal string, across the slope, was at right angles to the field at about. The receiving field was approximately on the sound channel axis laid between and.
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 masts. Each cable had special takeouts built into it at intervals from which wires to the hydrophones were connected. Each mast was clamped onto the special cable with takeouts. At the upper end of the approximately 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.