NUCLEAR, BIOLOGICAL AND CHEMICAL WEAPONS
March 12, 2014: The United States recently revealed that the refurbishment of its B61 nuclear bombs is proceeding but that budget cuts may delay the number to be refurbished (to about 400) and the delivery date (from 2017 to 2020). The B61 ground penetrating version is being fitted with the JDAM GPS guidance kit so that it can use a smaller warhead to get the same effect. Since JDAM lands the bomb within 30 meters of the aiming point a smaller nuclear explosion is needed to get the same effect (on an underground bunker) as the old version that would only land within 150 meters of the aiming point. That means you only need a 30 kiloton nuke to take out a bunker instead of a much larger one of about 150 kilotons. This means less collateral damage and fallout going into the atmosphere. Yes, even nukes can be ecologically sensitive.
Getting this refurb into service means that the last American megaton (million tons of TNT equivalent) bomb, the B83 can be retired before it ages out of usefulness. Nuclear weapons have electronic and chemical components that degrade with and either have to be refurbished or retired because of age-related ineffectiveness.
Back in 2006 the United States decided to refurbish one of its oldest warhead designs, the B61, which is comes is a thermonuclear ("H-Bomb") weapon that is available in several versions. The ones being refurbished are those designed for penetrating the earth before going off. Most nuclear bombs with higher yields ones (300-400 kilotons) are detonated in the air. The exact number of B61s being refurbed was a secret but was believed to be about half the current ones in service. Some 3,200 B61s were built since the design went into service in the mid-1960s, and about half of those remain available for use.
The refurbed warheads will be good for another two decades. The basic B61 nuclear bomb weighs 320 kg (700 pounds), is 330mm in diameter and 3.56 meters (11.7 feet) long. They are delivered by aircraft as bombs. Back in 2006 about 400 B61s were still stored in Europe and these are not being refurbed. Interestingly, the W80 nuclear weapon used on some two thousand cruise missile warheads are not being refurbished either. Without the refurb all these older warheads will be useless by the end of the decade and that fits in with the continuing arrangements between Russia and the United States to reduce their Cold War era nuclear arsenals.