Four years ago, the U.S. Department of Defense had 135,000 portable GPS receivers in service, plus many more embedded in weapons and equipment. Since then, the number has risen to over 200,000. But the troops still prefer to carry commercial GPS. There are two reasons for this. For the infantry, the biggest thing is that the commercial GPS devices are lighter. That is also the case with batteries in commercial GPS receivers lasting longer. That means you don't have to carry as many batteries. For troops that hike around a lot, mainly the infantry, every little bit helps when it comes to weight.
Over the last four years, the army has replaced more than 100,000 older (from the early 1990s) PLGR GPS receivers. These were replaced with the new $2,300 DAGR (Defense Advanced Global Positioning System Receiver), which weighs .45 kg (15 ounces), but is small enough (16.5x8.7x4cm/6 3/8x3 7/16x1 9/16 inches) to fit into a standard two-clip ammo pouch. DAGR can get its first position fix within 60 seconds, and can run continuously for twelve hours on its battery. There are a number of useful accessories, including an anti-jamming device, a more powerful antenna and external power cables. DAGR has one major advantage over commercial GPS receivers, it can use the Precise Positioning Service (PPS) signal. PPS allows users to operate reliably when someone is trying to jam GPS signals. But in Afghanistan and Iraq, the troops never encountered GPS jammers. So the infantry, whenever they could get away with it, left DAGR at home, and carried a commercial model.
DAGR also has the most popular features found in commercial GPS receivers, and can easily have its software updated. DAGR has a 43x58mm (1.7x2.3 inch) display, and can survive submersion into nearly 40 inches of water. The display is the major advantage of DAGR, as it can display more useful information, in map form, about where the troops are, and where they are going. The Department of Defense ordered 250,000 DAGRs, and still has a few of the older PLGRs in service. For troops in a vehicle, PLGR still does the job. The army wants to put a GPS unit (a PLGR will do) in every vehicle it has, especially the ones operating overseas.
The next generation GPS device is being designed, sort of. The DAGRs are expected to last for at least another few years. But with GPS being built into so many things, its difficult to know what features a special military GPS would have to have to justify the cost. GPS receivers are becoming a feature, not a separate piece of equipment.
GPS has changed warfare more than most people realize. It all happened during the 1990s, starting with the 1990-91 Gulf war. The U.S. Army, a pioneer in the use of radio on the battlefield, was still developing GPS when the Gulf War came along. What happened next was a complete surprise to the civilians who watched the war unfold. The GPS (Global Positioning System) provided precise location information (to within 25 meters or less) via a hand held satellite signal receiver. Not all the needed satellites were in orbit when war began, but there were enough up there to give coverage over most of the Gulf except for a few hours in the late afternoon. For an army operating in the desert, GPS was literally a lifesaver. It is very easy it is to get lost while traveling over (usually) unfamiliar terrain. Maps only appear to add to the confusion, and in desert operations, "navigation" becomes a major matter of life and death.
All that was changed in the Gulf War because of the GPS. This system provided precise location information to anyone with a battery powered SLGR (Small, Lightweight GPS Receiver, or "Slugger") unit. The smallest version weighed nearly a kilogram (two pounds). Knowing who (and what) is where on the battlefield is often a matter of life and death. Calling in artillery fire or air strikes depends on the ground observer (who is often not far from the target) knowing exactly where he is so that the shells or bombs hit the enemy and not friendly troops. Reconnaissance is much more effective with GPS, as the location of the target can be recorded with precision. Marking the location of enemy minefields, a common occurrence during the Persian Gulf War, was much more effective with GPS equipped units.
Some 4,500 GPS receivers were in the Gulf by the end of February, 1991, plus several hundred civilian versions bought by the troops (or their parents) at up to $4,000 each. At the end of the century you could buy a GPS receiver for a hundred dollars. Now, many people have GPS built into their cell phones. Basically the GPS is nothing more than a radio receiver that uses the signals from distant satellites to tell the user where he is. But it has changed military operations more than any other navigation device every employed by the troops.