war, the Viet Cong mainly sustained itself with captured arms; these were often of American manufacture or were crude, makeshift weapons used alongside shotguns made of galvanized pipes. Most arms were captured from poorly defended ARVN militia outposts. In 1967, all Viet Cong battalions were reequipped with arms of Soviet design such as the AK-47 assault rifle, carbines and the RPG-2 anti-tank weapon. Their weapons were principally of Chinese or Soviet manufacture. In the period up to the conventional phase in 1970, the Viet Cong and PAVN were primarily limited to 81 mm mortars, recoilless rifles, and small arms and had significantly lighter equipment and firepower in comparison with the US arsenal. They relied on ambushes, superior stealth, planning, marksmanship, and small-unit tactics to face the disproportionate US technological advantage. After the Tet Offensive, many PAVN units incorporated light tanks such as the Type 62, Type 59 tank., BTR-60, Type 60 artillery, amphibious tanks (such as the PT-76) and integrated into new war doctrines as a mobile combined-arms force. The PAVN started receiving experimental Soviet weapons against ARVN forces, including MANPADS 9K32 Strela-2 and anti-tank missiles, 9M14 Malyutka. By 1975, they had fully transformed from the strategy of mobile light-infantry and using the people's war concept used against the United States. The US service rifle was initially the M14. The M14 was a powerful, accurate rifle, but it was heavy, hard-recoiling, and especially unwieldy in jungle fighting, as it was unsuited for the combat conditions, often suffering from feed failure. It was gradually replaced by the M16 rifle, designed by Eugene Stoner, between 1964 and 1970. When first deployed, the M16 also suffered from a propensity to jam in combat, leaving the soldier defenseless and potentially killing him. According to a congressional report, the jamming was not related to operator error or to an inherent flaw in the rifle, but instead due to a change in the gunpowder to be used in the rifle's cartridges, which led to rapid powder fouling of the action and failures to extract or feed cartridges. This decision, made after "inadequate testing", proved that "the safety of soldiers was a secondary consideration." The issue was solved in early 1968 with the issuance of the M16A1, featuring a chrome-plated bore, which reduced fouling, and the introduction of a cleaner-burning powder. Incorporating features from the German FG-42 and MG-42, the U.S. replaced their earlier M1919 Browning in