Back in the 1990s, thermal sights for infantry weapons were unheard of. But now the second generation of these sights have been in combat for three years, and new models keep arriving with improvements in range, detail, zoom and reliability. Some of the latest models can be clipped on day sights, without requiring zeroing the combined sight all over again.
It was only four years ago that the second generation of thermal weapons sights began reaching the troops. The new sights revolutionized the way troops fight at night, since "thermals" sense heat, and are effective anywhere (the old night sights depended on amplifying available light). Thermal sights are particularly popular because they also identify any warm machinery, at long distance, by detecting heat, and they can be used in caves (and other places that lack any light to amplify) as well as in situations like sandstorms and fog.
The U.S. TWS I (officially the AN/PAS-13 weapons-mounted thermal sight) has been around for a nearly a decade, but the new version addresses a long list of user complaints and suggestions. Basically, TWS II is lighter, easier to use, and easier to keep supplied with batteries. The TWS II comes in three sizes; light (for M-16 type rifles, weighs .86 kg/1.9 pounds and is good out to 550 meters), medium (for light machine-guns, weighs 1.27 kg/2.8 pounds and is good out to 1,100 meters) and heavy (for .50 caliber weapons and 40mm grenade launchers, weighs 1.73 kg/3.8 pounds and is good out to 2,200 meters). The light sight batteries last 5-25 hours, while the heavier models are good for 6.5-18 hours.
Compared to TWS I, the new versions are about a third lighter, and use standard AA batteries. This was something the troops were emphatic about. TWS I used special batteries, which, too often, the users could not get replacements for. But you can always get AAs. Even during combat, troops have found local Iraqi or Afghan shops selling AAs, and were able to keep their electronic gear going as a result.
Over 20,000 TWS II sights have been produced so far. And everyone wants one. The army alone expects to eventually spend over $2 billion on new thermal sights, and it will be another three years before production catches up with demand for helmet and weapons mounted thermals.