The U.S. military is bringing back an "obsolete," 1960s era anti-tank weapon because it is a cheaper, and more portable, way to provide the infantry with some "portable artillery." The Department of Defense is buying 6,399 LAW (Light Anti-tank Weapon). Over 16,000 training rounds are being bought as well. These 7.7 pound, one-shot (the launcher is disposable) anti-tank rockets were a replacement for the World War II bazooka (similar to the Russian designed RPG).
However, by the 1970s, it was obvious that the LAW was not able to kill most modern tanks, and in late 1980s, was replaced by the AT4. However, the heavier (15 pounds), and more expensive AT4 ($2,700 per each disposable launcher and four pound warhead) is also larger (40 inches long and 3.3 inches in diameter.) Since American troops rarely faced enemy tanks, but did frequently need some additional firepower to deal with enemy infantry in bunkers or buildings, the AT4 was seen as a step backwards.
The LAW has several advantages. It is compact (20 inches long, 2.6 inches in diameter), light (7.7 pounds) and cheap (about $2,000 each). It's 2.2 pound warhead can still knock out light armored vehicles (and unarmored ones as well), but it most often used against enemy troops inside bunkers and buildings. For that job, the U.S. Department of Defense had bought the SMAW (Shoulder-Launched Multipurpose Assault Weapon). This was a 17 pound Israeli design (in response to the RPG). But the SMAW launcher costs $14,000, and each rocket costs more than their RPG equivalents (and are a bit more effective.) Actually, many troops have expressed an interest in just getting the RPG, which has a larger (6 pound) warhead, and is a lot cheaper (the RPG launcher goes for about $500 each, and the rockets can be had for under a hundred dollars each). However, the compactness of the LAW, and better accuracy, does make a difference on the battlefield, and is considered worth the cost. The LAW is simple, light, easy-to-use and relatively cheap. It's hard to improve on that, which is why the LAW is making a comeback. Actually, it never went away in many other armies.