The U.S. military has been using a growing number of simulators for training. For many decades the only simulator was the flight simulator, although the army, marines and navy constructed crude, by current standards, mechanical or electro-mechanical simulators of some equipment (parts of weapons or ships). The value of these simulators was monitored by looking at the result of training tests everyone is constantly subjected to. If those who spent time on the simulators performed better, on average, than those who did not than the simulator was a success and more were used. This method was not unique to the military because they adopted much of this simulation technology from commercial firms that have to train people for complex tasks. Rather than have people practice on the actual equipment, and risk making mistakes that can ruin expensive machinery, some form of simulator was increasingly used.
Flight simulators have always led the way in simulator technology because aircraft have always been the most expensive equipment you have to train operators for. The development of flight simulators began in the 1930s. Back then, the simulators were much more primitive, and were used to teach pilots how to fly, and navigate, at night. It was much cheaper, and safer, to do this kind of training on the ground, via a simulator. Even today, the main emphasis with simulators is handling in-flight emergencies. Most actual missions tend to be rather uneventful most of the time. But many emergencies can crop up, if only rarely, so the pilots have a safe way to practice handling common, and not so common, emergencies via simulators.
New technology has made flight simulators a lot more effective and cheaper. Until a decade ago, a realistic combat flight simulator cost about as much as the aircraft it was simulating. While that did reduce the cost (per "flying" hour) of pilots practicing, it was not enough of a savings to make it practical for less wealthy countries to get these simulators and use them heavily. Thus we had a continuation of the situation where countries could scrape together enough money to buy high performance aircraft, but not enough to pay for all that flight time needed to make their pilots good enough to face aerial opponents (especially the Americans).
The new generation of simulators cost up to a tenth of the price of the aircraft they simulate. Suddenly, countries like China can buy dozens of simulators, and give their pilots enough realistic training to make them a threat in the air (at least to Western pilots). Each of these simulators can be run about 6,000 hours a year. While a hundred hours a year in a simulator isn't a complete replacement for a hundred hours of actual air time, it's close enough if the training scenarios are well thought out. And another 40-50 hours of actual air time a year gives you a competent pilot. Add another few hundred hours using commercial (game store bought) flight simulators (especially when played in groups via a LAN), and you have some deadly pilots. The Chinese have, since the 1990s, stressed the use of PCs as a foundation for cheaper and more powerful simulators. Now they have an opportunity to really cash in on this insight.
When personal computers appeared in the 1970s the military soon realized that this made it possible to develop simulators for non-flight operations. At first it was more accurate vehicle simulators. After the explosion of new (smaller, more powerful, cheaper and reliable) computer technology in the 1990s it slowly became possible to build simulators for activities like infantry combat which were long believed to be beyond simulation technology. Again, because personnel in all the services are regularly tested for the skills they require for their job (be it combat or some form of administration or support) it was a simple matter to separate the troops who used the new simulators from those who were not and compare the skill levels.
An example of how this worked in wartime was seen in 2004 when the Sunni Islamic terrorists in Iraq began using a lot of roadside bombs and ambushes. The army had encountered this weapon before and the solution was specific skills for detecting and dealing with these weapons. Several simulators were quickly developed and put to use. The troops who used the simulators were tested for the combat skills acquired and the simulators were found to quickly impart these skills. Troops using dangerous roads performed more effectively and suffered fewer losses once they had used the simulators. Around the same time the army also developed firing range simulators, using actual weapons rigged to send out an electronic signal at a movie screen size display of a combat situation. The rifles and pistols were also rigged to provide realistic recoil, which throws off aim a bit for the next shot. Troops using these virtual rifle ranges were found to be much more proficient when they took real weapons out and were tested with live ammo.
The cheaper and more powerful simulator technology has made it possible to build simulators for larger aircraft, with larger crews. The U.S. Navy is using a P-8A (maritime patrol aircraft) full-flight simulator that can accurately replace flight training in an actual aircraft. For the last few decades, simulators have been increasingly replacing training in the air. Even the U.S. Army is using such simulators to train the crew of transport helicopters. The navy has built simulation software into its ships combat systems, allowing weapons crews to train together under realistic conditions without actually firing the expensive missiles they use.
Back in 2010 Israel even formed a training squadron that consisted solely of flight simulators. The eight Israeli made simulators, each with an F-16 cockpit and all encompassing video displays, are used to train groups of pilots in combined combat exercises. In these situations, two of the simulators are used to represent enemy aircraft. By having all the simulators in one place, communications problems would be eliminated. For several decades now, simulators participated in these joint exercises, even though each simulator would be in a different location. But this could be disrupted if there were problems with the communications link. This could either be (rarely), the link going down. More commonly, the link would slow down the signals, which meant pilots were out of sync, and the illusion of operating in the same air space was degraded. Israel is also moving all its flight simulators to one air base, both to make maintenance easier and to deal with these communications risks. As a small country, putting all the flight simulators in one place does not put a big travel burden on pilots. Pilots using this system obtain valuable skills cheaply. These new skills are tested and verified the next time the pilots go up in the actual aircraft.