On Target

Looking forward to the day when it will have its own intermediate-range (1,500-mile) Fleet Ballistic Missile (the IRBM), the Navy this week placed in commission an experimental vessel named the Compass Island. The ship is jammed with feather-sensitive navigational equipment. The Island's mission: to test a navigational system capable of making the continuous hairline computations necessary to missile launching at sea.

The problem that has plagued Navy missile men up to now has been how to determine exactly and continuously where the ship is located on the earth's surface. At 1,500-mile range, such positioning becomes tremendously important to the missile's accuracy. Even under ideal launching conditions, missile men admit an intermediate missile is unlikely to hit closer than a quarter of a mile from the bull's-eye. If determinations of the target's direction and the ship's position are slightly off, the error can be disastrously larger. What makes the problem particularly difficult on shipboard is that the launching platform is continually moving.

The Compass Island is a 17,600-ton converted merchantman, commanded by James A. Dare. Without reference to any shore-based aids, the Ship's Inertial Navigational System (SINS), designed by M.I.T.'s Dr. Charles S. Draper, will furnish continuous position reports, the location of true north and the ship's speed. Essentially a superrefined gyroscopic system, SINS is self-correcting and will be continuously checked for accuracy against a star-tracker.

The bulk of the SINS equipment is housed in a 67-ton, temperature-controlled navigational tower that looms just forward of the superstructure in the most rigid part of the ship. To protect the instruments from as much motion as possible, the Compass Island is equipped with wing-shaped gyrofins, which cut down roll from 7 1/2DEG to a barely perceptible .4DEG. Among the ship's other refinements: a giant, airfoil-shaped sonar dome beneath the keel that will measure ship's speed (and which has already earned the nickname "droop snoot").

Although all of Compass Island's instruments have been laboratory-tested, they have never before been tested at sea or linked together to form a whole system. With observing scientists from M.I.T. and Sperry Gyroscope aboard, Compass Island will put to sea in January to test SINS' accuracy in familiar Atlantic coastal waters. After that it will put back into port periodically to take on new equipment for testing. If the system functions as well as the Navy hopes, it may well be installed aboard submarines and other missile-launching vessels by the summer of 1958.

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