Research was conducted on groups of unattended vehicles performing some collaborative tasks. Navigation of these vehicles and more specifically, knowing each other's position, is mandatory. In densely built environments, forests, etc., GPS is not always available or accurate. Using information about encounters between the vehicles may significantly improve position information. Detecting encounters can be done very easily with low cost sensors. TNO developed and patented an innovative technology that uses information on encounters to improve the position information. The first promising results show that information on encounters can be used in standard integrated INS/GNSS navigation systems to aid the navigation solution. To increase the number of encounters, a group of unattended vehicles may deliberately try to encounter each other if their navigation solution becomes less certain during GNSS outages.