By the 1960s, after becoming involved in war in Vietnam, the U.S. did an abrupt about-face and decided to standardize on the intermediate 5.56×45mm round (based on the .223 Remington varmint cartridge) fired from the new, lightweight M16 rifle, leaving NATO to hurry and catch up. Many of the NATO countries could not afford to re-equip so soon after the recent 7.62mm standardization, leaving them armed with full-power 7.62mm battle rifles for some decades afterwards, although by this point, the 5.56mm has been adopted by almost all NATO countries and many non-NATO nations as well. This 5.56mm NATO round was even lighter and smaller than the Soviet 7.62×39mm AK-47 cartridge but possessed higher velocity. In U.S. service, the M16 assault rifle replaced the M14 as the standard infantry weapon, although the M14 continued to be used by designated marksmen. Although at 20", the barrel of the M16 was shorter than that of the M14, it was still designated a "rifle" rather than a "carbine", and it was still longer than the AK-47, which used a 16" barrel. (The SKS – an interim, semi-automatic, weapon adopted a few years before the AK-47 was put into service – was designated a carbine, even though its 20" barrel was significantly longer than the AK series' 16.3". This is because of the Kalashnikov's revolutionary nature, which altered the old paradigm. Compared to previous rifles, particularly the Soviets' initial attempts at semi-automatic rifles, such as the 24" SVT-40, the SKS was significantly shorter. The Kalashnikov altered traditional notions and ushered in a change in what was considered a "rifle" in military circles.)