The TWS I (officially the AN/PAS-13 weapons-mounted thermal sight) has been around for a few years, 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 1.9 pounds and is good out to 550 meters), medium (for light machine-guns, weighs 2.8 pounds and is good out to 1,100 meters) and heavy (for .50 caliber weapons and 40mm grenade launchers, weighs 3.8 pounds and is good out to 2,200 meters).
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 shops selling AAs, and were able to keep their electronic gear going as a result.
Thermal sites, unlike the older night-vision devices (which amplified any available light), illuminate people, and any warm machinery, by detecting heat. Thus thermal sights can be used in caves (and other places that lack any light to amplify) as well as in situations like sandstorms and fog.
Currently, some 7-8,000 TWS II sights a year are being produced. And everyone wants one.
The second generation of thermal weapons sights began reaching the troops late last year, and now everyone wants them. For example, the U.S. Marines just announced that they will be equipping the .50 caliber machine-gun on their M-1 tanks with the sight.