most roles with the M60 machine gun, including on helicopters where it was used for suppressive fire. While its issues were not as severe as they were in the M14 or M16, the M60 still could fail to fire at crucial times – spent casings could get stuck inside of the chamber, meaning the barrel would have to be replaced before it could fire again. The AC-130 "Spectre" Gunship and the UH-1 "Huey" gunship were used frequently by the U.S. during the war. The AC-130 was a heavily armed ground-attack aircraft variant of the C-130 Hercules transport plane, while the Huey is a military helicopter powered by a single, turboshaft engine; approximately 7,000 UH-1 aircraft saw service in Vietnam. The U.S. heavily armored, 90 mm M48A3 Patton tank saw extensive action during the Vietnam War, and over 600 were deployed with U.S. Forces. US ground forces also had access to B-52 and F-4 Phantom II and other aircraft to launch napalm, white phosphorus, tear gas, chemical weapons, precision-guided munition and cluster bombs. Radio communications The Vietnam War was the first conflict where U.S. forces had secure voice communication equipment available at the tactical level. The National Security Agency ran a crash program to provide U.S. forces with a family of security equipment, codenamed NESTOR, fielding 17,000 units initially; eventually 30,000 units were produced. However, limitations of the units, including poor voice quality, reduced range, annoying time delays and logistical support issues, led to only one unit in ten being used. While many in the U.S. military believed that the Viet Cong and PAVN would not be able to exploit insecure communications, interrogation of captured communication intelligence units showed they could understand the jargon and codes used in real time and were often able to warn their side of impending U.S. actions. Extent of U.S. bombings The U.S. dropped over 7 million tons of bombs on Indochina during the war, more than triple the 2.1 million tons of bombs the U.S. dropped on Europe and Asia during all of World War II and more than ten times the amount dropped by the U.S. during the Korean War. 500 thousand tons were dropped on Cambodia, 1 million tons were dropped on North Vietnam, and 4 million tons were dropped on South Vietnam. On a per capita basis, the 2 million tons dropped on Laos make it the most heavily bombed country in