SIMNET: Первая в мире оперативная система виртуальной реальности для военных тренировок.

SIMNET was a wide area network with vehicle simulators and displays for real time distributed combat simulation: tanks, helicopters and airplanes in a virtual battlefield. SIMNET was developed for and used by the United States military. SIMNET development began in the mid 1980s, was fielded starting in 1987, and was used for training until successor programs came online well into the 1990s. SIMNET was perhaps the world's first fully operational virtual reality system and was the first real time, networked simulator. It was not unlike our massive multiplayer games today. It supported a variety of air and ground vehicles, some human directed and others autonomous.

Jack Thorpe of the Defense Advanced Research Projects Agency (DARPA) saw the need for networked multi user simulation. Interactive simulation equipment was very expensive, and reproducing training facilities was likewise expensive and time consuming. In the early 1980s, DARPA decided to create a prototype research system to investigate the feasibility of creating a real time distributed simulator for combat simulation. SIMNET, the resulting application, was to prove both the feasibility and effectiveness of such a project. Training using actual equipment was extremely expensive and dangerous. Being able to simulate certain combat scenarios, and to have participants remotely located rather than all in one place, hugely reduced the cost of training and the risk of personal injury. Long haul networking for SIMNET was run originally across multiple 56 kbit/s dial up lines, using parallel processors to compress packets over the data links. This traffic contained not only the vehicle data but also compressed voice.

SIMNET was developed by three companies: Delta Graphics, Inc.; Perceptronics, Inc.; and Bolt, Beranek and Newman (BBN), Inc. There was no prime contractor on SIMNET; independent contracts were made directly with each of these three companies. BBN developed the vehicle simulation and network software, as well as other software such as artillery, resupply, and semi automated forces often used for opposing forces. Delta Graphics, based in Bellevue, Washington, developed the graphics system and terrain databases. Delta Graphics was eventually bought by BBN. Perceptronics, based in Los Angeles, was responsible for the actual SIMNET simulators; the company's engineers, human factors personnel and manufacturing team designed, developed and built over 300 full crew simulators, integrating the controls, sound systems and visual systems into the special simulator shells; they also installed the simulators in a number of facilities in the US and Germany, trained the operators and supported the system for several years. BBN was responsible for developing the dynamic simulation software for each of the simulators, as well as the distributed networking communication software that kept each simulator informed of the position (and other state information) of other simulators that were within potential line of sight within the shared virtual environment. Each simulator maintained its own copy of this virtual environment, and broadcast its own state information to the other simulators.

Since this was a networked simulation, each simulation station needed its own display of the shared virtual environment. The display stations themselves were mock ups of certain tank and aircraft control simulators, and they were configured to simulate conditions within the actual combat vehicle. The tank simulators, for example, could accommodate a full four person crew complement to enhance the effectiveness of the training. The network was designed to support up to several hundred users at once. The fidelity of the simulation was such that it could be used to train for mission scenarios and tactical rehearsals for operations performed during the U. S. actions in Desert Storm in 1992. SIMNET used the concept of “dead reckoning” to correlate the positions of the objects and actors within the simulated environment. Duncan (Duke) Miller, the BBN SIMNET program manager, first used this term, which harks back to the earliest days of ship navigation, to explain how simulators were able to communicate state change information to each other while minimizing network traffic. Essentially, the approach involves calculating the current position of an object from its previous position and velocity (which is composed of vector and speed elements). The SIMNET protocols provided that whenever the true state of a simulator deviated by more than a certain threshold from its state as computed by dead reckoning, the simulator was obligated to send out a new state update message. The use of SIMNET protocols and SIMNET based training systems in the First Gulf War demonstrates the success of the SIMNET, and its legacy was viewed as proof that realtime interactive networked cooperative virtual simulation is possible for a large user population. Later, the Terrestrial Wideband Network (a high speed descendant of the ARPANET that ran at T1 speeds) was used to carry traffic. This network remained under DARPA after the rest of ARPANET was merged with NSFNet and the ARPANET was decommissioned.

SIMNET was actively used by the U. S. Army for training primarily at Fort Benning, Fort Rucker, and Fort Knox. Additional temporary and permanent locations were in Fort Leavenworth and Grafenwoehr, Germany. It was also used to test vehicles still in development.

The follow on protocols to SIMNET were called Distributed Interactive Simulation; the primary U. S. Army follow on program was the Close Combat Tactical Trainer (CCTT). The SIMNET D (Developmental) program used simulation systems developed in the SIMNET program to perform experiments in weapon systems, concepts, and tactics. It became the Advanced Simulation Technology Demonstration (ADST) program. It fostered the creation of the Battle Labs across the US Army, including the Mounted Warfare TestBed at Ft Knox, Ky, the Soldier Battle Lab at Ft Benning, GA, the Air Maneuver Battle Lab at Ft Rucker, AL, the Fires Battle Lab at Ft Sill, OK.

Additional research programs after the end of SIMNET included work in weather and real time terrain modifications.