Page "Transit (satellite)" Paragraph 19

If the receiver was also moving relative to the earth, such as aboard a ship or airplane, this would cause mismatches with the idealized Doppler curves, and degrade position accuracy.

However, positional accuracy could usually be computed to within 100-meters for a slow-moving ship, even with reception of just one two-minute Doppler curve.

This was the navigation criterion demanded by the U. S. Navy, since American submarines would normally expose their UHF antenna for only 2-minutes to obtain a usable Transit fix.

The U. S. Submarine version of the Transit System also included a special encrypted ( and more accurate ) version of the downloaded satellite's orbital data.

This enhanced data allowed for considerably enhanced system accuracy ( not unlike Selective Availability < SA > under GPS ).

Using this enhanced mode accuracy was typically less than 20 meters.

( Between LORAN C and GPS.

) Certainly, the most accurate navigation system of its day.