What I can add to LWs reply based on articles probably 30 years ago, TERCOM worked by updating its system in a fix box. The box would be of finite length and sensors only need to radiate in the box.
As crucial to the missiles system was mapping accuracy. In the mid-80s global mapping was at 100 m intervals. For fix boxes they needed 10 m. The aim then was to improve global data to 10 m. The last I heard was that it was considerably better than that. You can see that the improvement from 100 to 10 was an increase of 100 times. To 1 m an increase of 10,000 times.
Last edited by Pontius Navigator; 26th Nov 2018 at 18:34.