Nearly all United States-allied forces were armed with U.S. weapons, some of which, such as the M1 Carbine, were substitute standard weapons dating from World War II. The Australian army employed the 7.62 mm L1A1 Self-Loading Rifle as their service rifle, with the occasional US M16.
The NVA, although having inherited a variety of American, French, and Japanese weapons from World War II and the First Indochina War (aka French Indochina War), were largely armed and supplied by the People's Republic of China, the Soviet Union, and its Warsaw Pact allies. In addition, some weapons—notably anti-personnel explosives, the K-50M (a PPSh-41 copy), and “home-made” versions of the RPG-2—were manufactured in Vietnam. By 1969 the US Army had identified 40 rifle/carbine types, 22 machine gun types, 17 types of mortar, 20 recoilless rifle or rocket launcher types, 9 types of antitank weapons, and 14 anti-aircraft artillery weapons used by ground troops on all sides. Also in use, primarily by anti-communist forces, were the 24 types of armored vehicles and self-propelled artillery, and 26 types of field artillery & rocket launchers.
Communist forces were principally armed with Chinese and Soviet weaponry though some Viet Cong guerrilla units were equipped with Western infantry weapons either captured from French stocks during the first Indochina war or from ARVN units or requisitioned through illicit purchase.
The ubiquitous Soviet AK-47 was widely regarded as the best assault rifle of the war and it was not uncommon to see U.S. special forces with captured AK-47s.
The American M16 rifle, which replaced the M14, was lighter and considered more accurate than the AK-47 but was prone to jamming. Often the gun suffered from a jamming flaw known as "failure to extract," which meant that a spent cartridge case remained lodged in the chamber after a bullet flew out the muzzle. According to a congressional report, the jamming was caused primarily by a change in gunpowder which was done without adequate testing and reflected a decision for which the safety of soldiers was a secondary consideration.
The heavily armored, 90 mm M48A3 Patton tank saw extensive action during the Vietnam War and over 600 were deployed with US Forces. They played an important role in infantry support though there were few tank versus tank battles. The M67A1 flamethrower tank (nicknamed the Zippo) was an M48 variant used in Vietnam. Artillery was used extensively by both sides but the Americans were able to ferry the lightweight 105 mm M102 howitzer by helicopter to remote locations on quick notice. With its 17-mile (27 km) range, the Soviet 130 mm M-46 towed field gun was a highly regarded weapon and used to good effect by the NVA. It was countered by the long-range, American 175 mm M107 Self-Propelled Gun.
The United States had air superiority though many aircraft were lost to surface-to-air missiles and anti-aircraft artillery. U.S. air power was credited with breaking the siege of Khe Sanh and blunting the 1972 Communist offensive against South Vietnam. At sea, the U.S. Navy had the run of the coastline, using aircraft carriers as platforms for offshore strikes and other naval vessels for offshore artillery support. Offshore naval fire played a pivotal role in the Battle for the city of Hue, providing accurate fire in support of the U.S. counter-offensive to retake the city.
The Vietnam War was the first conflict that saw wide scale tactical deployment of helicopters. The Bell UH-1 Iroquois was used extensively in counter-guerilla operations both as a troop carrier and a gunship. In the latter role, the "Huey" as it became affectionately known, was outfitted with a variety of armaments including M60 machineguns, multi-barreled 7.62 mm Gatling guns and unguided air-to-surface rockets. The Hueys were also successfully used in MEDIVAC and search and rescue roles.
Weapons of the ARVN, US, South Korean, Australian, and New Zealand Forces
Pistols & revolvers
Browning High Power pistol - used by Australian and New Zealand forces. Also used on an unofficial basis by US Reconnaissance and Special Forces units.
M16 and M16A1 - The M16 was issued in the late 1960s, but due to reliability issues, it was replaced by the M16A1 which added the forward assist and chrome-lined barrel to the rifle for increased reliability.
XM177E2 - Shortened version of the M16 rifle very popular with MACV-SOG units
Heckler & Koch HK33 - It was used by Thai forces that were not armed by the United States. It was chambered for the same cartridge as the M16 assault rifle used by American troops.
T223 - which is a copy of the Heckler & Koch HK33 Assault Rifle under license by Harrington & Richardson used in small numbers by Navy SEAL teams. Even though the empty H&R T223 was 0.9 pounds (0.41 kg) heavier than an empty M16A1, the weapon had a forty-round magazine available for it and this made it attractive to the SEALS.
Thompson submachine gun - It was used in small quantities by artillery and helicopter units. Even though it was replaced in the end of the Korean war after serving in WW2, it was still used by many American troops and South Vietnamese troops in the Vietnam war. The Viet Cong were armed with the Chinese copy.
M3 Grease gun - The M3 "Grease gun" was issued to troops all over Vietnam was the main submachine gun, but many others were used such as the Thompson which was replaced later on.
Swedish K - It was used by Navy SEALs in the beginning of the war, but was later replaced by the Smith & Wesson M76 in the late 1960s. Many South Vietnamese soldiers were armed with this weapon and used it until the end of the war.
Smith & Wesson M76 - A copy of the Swedish K, it replaced that gun as the main submachine gun of the Navy SEALs in 1967.
Madsen M-50 - It was supplied by mercenaries from Denmark and a lot were bought by the United States for the Army of the Republic of Vietnam.
Uzi (SOG recon teams) The Uzi submachine gun was supplied in from Israel and given to special forces troops in the field.
Owen Gun (Australian submachine gun) It served the Australian Army through WWII, Korea, Malaya and now into the Vietnam War as the main submachine gun. It was later replaced by the F1 submachine gun that resembled it.
Sten submachine gun - This weapon was used by Special Forces troops with silencers attached to the weapon's barrel.
The shotguns were used as an individual weapon during jungle patrol; infantry units were authorized a shotgun by TO & E (Table of Organization & Equipment). Shotguns were not general issue to all infantrymen, but were select issue, such as one per squad, etc.
M34 white phosphorus grenade is a smoke grenade that uses white phosphorus, which, when in contact with air ignites and creates white smoke. The white phosphorus was also a useful way to dislodge the Viet Cong from tunnels or other enclosed spaces as the burning white phosphorus absorbs oxygen, causing the victims to suffocate or suffer serious burns.
M79 Grenade Launcher, a single shot grenade launcher that uses the 40mm grenade used against vehicles or material. It is break action similar to a shotgun it had leaf iron sights and was accurate up to 150 yards. The China Lake Grenade Launcher, a pump action weapon, also saw action in the Vietnam War albeit in very small numbers.
M203 grenade launcher, The M203 is a single shot 40 mm under-slung grenade launcher designed to attach to a rifle. It uses the same rounds as the older stand-alone M79 break-action grenade launcher, which utilizes the High-Low Propulsion System to keep recoil forces low. Though versatile, and compatible with many rifle models, the M203 was originally designed for the U.S. M16.In the Vietnam war U.S. Navy and Coast Guard personnel on boats would lob M203 grenades into the water (using the M79 grenade launcher), this to preemptively attack Viet Cong swimmers ("sappers") attempting to plant explosives on anchored or moored U.S. water craft 
NVA (North Vietnamese Army) and the Southern communist guerrillas NLF, or Viet Cong as they were commonly referred to during the war, largely used standard Warsaw Pact weapons. Weapons used by the North Vietnamese also included Chinese Communist variants, which were referred to as CHICOM's by the US military.
North Vietnamese SAM crew in front of a SA-2 launcher.
SVD-63 semi-automatic marksman rifle, also known as the "Dragunov" sniper rifle
MAS-36 rifle Captured French rifle from first Indochina War, used by NVA in earlier stages of the Vietnam War
MAS-49 rifle Captured French rifle from first Indochina War, used by NVA throughout the 1950's and up to the mid 1960's
Mosin–Nagant bolt-action rifles and carbines (from the Soviet Union, Warsaw Pact countries, and the People's Republic of China)
Mauser Kar98k bolt-action rifle (many of the Mausers used by the VPA and the NLF were from rifles captured from the French during the First Indochina War and rifles provided to them by the Soviets as military aid)
Walther PPK German pistol captured during World War II by the Soviet Army, supplied to the Viet Cong in very limited amounts
Tokarev TT-33 - Soviet-designed double/single-action 7.62x25mm semi-automatic pistol. More commonly used were the Chinese variants of the T33, known as the Type-51 and Type-54. Carried by NVA and Viet-Cong officers, it accepted an 8 round single stack box magazine.
Makarov PM - Soviet-designed double/single-action 9x18mm Makarov (9.5x18mm) semi-automatic pistol. Reproduced in China as the Type-59, this small and reliable pistol became the standard sidearm of communist forces in Europe and Asia. Utilizing a simple blow-back action, this self-loading pistol fed from an 8 round single stack box magazine.
The Vietcong were not always able to be supplied by the PAVN. They sometimes took weapons from US soldiers after an attack or raided US or South Vietnamese weapon stockpiles. This increased the number of weapons available and gave balance against the US arsenal
Citations and notes
^Bart Hagerman, USA Airborne: 50th Anniversary, Turner Publishing Company, p.237