In the last century, fatigue from lack of sleep have become recognized as a major problem in combat. Recently, the U.S. Army issued a medical report that concluded it was essential that troops in combat get at least 7-8 hours of sleep a day, for optimal performance. Decades of practical experience has led U.S. commanders to realize that better sleeping conditions, and living conditions in general, make for better performance in combat. That's why combat troops in Iraq and Afghanistan often sleep in air conditioned quarters, have Internet access, lots of amenities, and a two week vacation (anywhere) in the middle of their combat tour.
A lot of this wisdom came from generations of NCOs noting that troop performance improved noticeably if soldiers got enough sleep. Troops in the combat zone were told "sleep every chance you get," and experienced NCOs took measures to help this happen. This included shielding the slumbering soldiers from officers who might view such seeming sloth as a bad thing. But now it's official, if you want your troops to be more effective in combat (including reducing friendly fire incidents and errors in judgment), make an effort to ensure as much sleep as possible. Thus the air conditioned sleeping accommodations for combat troops proved to be a key factor in the effectiveness of U.S. troops (both combat and support.) Combat troops might go weeks, or months, without the air conditioned sleeping quarters, when they were outside the wire for extended periods. But getting back to the more comfortable sleeping quarters was a big boost for morale, and effectiveness. It was something to look forward to.
But there are many times when the action is so relentless that there is simply not much time for sleep. Thus for most of the last century, troops have had access to drugs that keep them alert after long hours in combat. This fatigue problem has particularly acute as battles became endurance contests, with forces engaged for days on end.
For over a century, the solution has been amphetamines ("speed"). However, this drug can impair judgment, making the user more aggressive, for example. In the last decade, kinder and gentler medications have become available. The most effective of these has been Modafinil (sold as Provigil). This stuff is described as "a mood-brightening and memory-enhancing psychostimulant which enhances wakefulness and vigilance." Tests showed that user performance was degraded 15-30 percent, versus 60-100 percent for those who took nothing at all after 24 hours of being awake. While the Modafinil did a pretty good job, the dextroamphetamine was still a bit better. So amphetamines remained competitive.
A new stimulant, apparently superior to dextroamphetamine and Modafinil, is being tested. This is CX717. Another approach, and another new drug, Gaboxadol, make small amounts of sleep provide the same effect as a full nights sleep. Thus a soldier could nap for an hour or less, and be ready for another full day of action. But Gaboxadol ultimately failed to work because of side effects and inability to consistently deliver the desired results. Gaboxadol did point the way towards work on better drugs to do what Gaboxadol showed was possible.
Wakefulness can be a potent weapon, especially for commandos, or troops engaged in prolonged combat (like the Battle of Fallujah in 2004). Without these wakefulness drugs, you would have to either pull troops out of action so they could rest, or leave them in and risk having them make fatal mistakes. Either way, you have a problem, because there are never enough troops to get the job done. But with the wakefulness medications, you can solve the problem, for a few days, anyway. Prolonged use of these drugs is not healthy. But neither is being drowsy during combat.