Nation: THE FERRET FLEETS

Blandly classified as an “environmental research” vessel, the U.S.S. Pueblo is actually one of more than 80 immensely sophisticated ELINT (for electronic intelligence) ships in the U.S. Navy. That ferret fleet is intended as a counterforce to Russia’s 60-vessel ELINT armada, made up mostly of converted trawlers and hydrographic craft, all bristling with antennas and sensitive snooping gear. Just as the Pueblo and her kin prowl the international waters off China, North Korea and the Soviet Union, Russian trawlers are stationed off California, South Carolina, Florida’s Cape Kennedy, Guam and Alaska. A Soviet spy ship dogs every move of U.S. aircraft carriers on “Yankee Station,” the 45,000-sq.-mi. area of the Tonkin Gulf from which American air strikes over North Viet Nam originate, flashing alerts to Hanoi. Other Russian ELINT ships shadow the U.S. Sixth Fleet in the Mediterranean.

A main mission for both ELINT fleets is the systematic collection and classification of submarine “signatures”—the distinctive electronic blend of propeller and engine noises, wake turbulence and magnetic fields generated by each individual sub. Thanks to Pueblo & Co., the Navy has nearly completed a computer-taped “library” classifying Russia’s 450 or more subs, from diesel-powered Whiskey-class boats to the new, nuclear Juliett class. In the near future, U.S. naval commanders will be able to draw instant digital readouts that will identify any Soviet sub they can hear.

Pueblo’s unprepossessing, 179-ft.-long hull is fitted out with the latest in sophisticated ELINT equipment—globe-girdling single-side-band radio, hyperaccurate radars, sonars and navigation instruments. Another primary aim of the “spook ships”—espionage satellites like Samos and spy planes like the U-2 —is to be “painted” or “illuminated” by enemy radar, whose beams fall on the ship’s sensitive receivers. Those signals are taped and sent back to Washington for detailed analysis. By charting radar pulse repetition rates and frequencies, intelligence officers can identify the electronic signalings of known radar systems and thus roughly determine enemy dispositions, while radio traffic analysis provides information on troop buildups or movements and even the names of enemy commanders. Such data also permit the development of jamming programs.

To locate radar and radio sources, Pueblo employed the twin antennas mounted forward of the wheelhouse. Domelike direction finders and “tropo-scattering” sensors (which can “read” signals bouncing from the troposphere) are mounted on the foremast to analyze those signals and to eavesdrop on radio communications. The ship is equipped to test salinity levels, temperatures and algae growth in various parts of the Sea of Japan—all valuable information for sonar operators. Pentagon photos of Pueblo taken after the ship’s renovation in Bremerton, Wash., show advanced low-frequency antennas that would permit the ship to communicate with U.S. nuclear subs to a depth of about 100 feet.

Photographs cannot show Pueblo’s most sensitive gear, which is below the water line. From keel to boot topping, the hull bulges with sonar domes, hydrophones, subsurface antennas, and possibly a “giant ear” like that used on the larger U.S.S. Liberty, which was shot up by the Israelis in the Mediterranean last summer. Pueblo is also rigged to tow hundreds of yards of hydrophone cable with which to hear submarines as much as 75 miles away.