A description is given of the Position Location Reporting System (PLRS), which provides position location, tracking, and reporting for communities of hundreds of cooperating users in a tactical environment. PLRS uses time-of-arrival measurements aided by barometric pressure measurements to establish position tracking of these large communities of user terminals. The system uses the positions of a few user terminals as grid references, so that all positions are available both to the cooperating users and to command centers. All control, measurement reporting, and data exchange are cryptographically secured in a synchronous antijam communications network. Testing with live communities of 50 or more user terminals has been conducted at many sites throughout the US and in West Germany, with consistently good results. In addition, testing has been accomplished with computer-simulated communities of up to 380 user terminals. Recent live testing has successfully demonstrated an automated GPS interface for operation without fixed grid reference units. Results are presented, with an emphasis on position accuracy tests. >