BendixKing KMD 150 - Pilots Guide - Manual (Page 164)

150
Rev 2 Oct/2002 KMD 150 Pilot's Guide
The only time the DOD can predict there may be a substantial break in
coverage for civilian users, is at a time of National Emergency, when the
whole system may be reverted to P code (military) operation only, for
strategic reasons.
How Does GPS Work?