Later, even lighter carbine variants of many of these short-barreled assault rifles came to be adopted as the standard infantry weapon. In much modern tactical thinking, only a certain number of soldiers need to retain longer-range weapons, serving as designated marksmen. The rest can carry lighter, shorter-ranged weapons for close quarters combat and suppressive fire. This is basically a more extreme extension of the idea that brought the original assault rifle. Another factor is that with the increasing weight of technology, sighting systems, ballistic armor, etc., the only way to reduce the burden on the modern soldier was to equip them with a smaller, lighter weapon. Also, modern soldiers rely a great deal on vehicles and helicopters to transport them around the battle area, and a longer weapon can be a serious hindrance to entering and exiting these vehicles. Development of lighter assault rifles continued, matched by developments in even lighter carbines. In spite of the short barrels of the new assault rifles, carbine variants like the 5.45×39mm AKS-74U and Colt Commando were being developed for use when mobility was essential and a submachine gun was not sufficiently powerful. The AKS-74U featured an extremely short 8.1" barrel which necessitated redesigning and shortening the gas-piston and integrating front sights onto the gas tube; the Colt Commando was a bit longer, at 11.5". Neither was adopted as standard issue, although the U.S. did later adopt the somewhat longer M4 carbine, with a 14.5" barrel.