The B-61 is an unguided gravity bomb whose design dates back to the early 1970's. It has a maximum yield of 340 kilotons, about 34 times that of the bomb that destroyed Hiroshima.
As David writes:
Although it has never been used in action, some forty years in service ought to indicate that it is fairly satisfactory, and they are all built and paid for.I can understand why the Pentagon might want to add precision guidance packages to these bombs. While David makes a good point that WWII-era bomb sights were good enough, the biggest problem is that the aircraft carrying them still has to fly over the target to drop the weapon. Turning the B-61 into a PGM (Precision Guidance Munition), the need to fly over the target is greatly reduced, if not eliminated, which in turn reduces the danger to the crew of the aircraft carrying it.
In Washington there is a move afoot to spend another $10 billion dollars on the B-61's. The Air Force wants to add a guidance system to improve accuracy. We really need that. These are nukes, with a total destruction radius measured in miles. Get the bomb with a mile or so of the aim point, and that target is vaporized. World War II mechanical bomb sights were good enough for that.
Another point to make about the B-61 maintenance and upgrade program was expressed in this comment I made to David's post:
Nuclear weapons, and in particular fusion warheads, aren't like other weapons systems. They age and require refurbishment, particularly the deuterium and/or tritium that is the 'H" in 'H-Bomb'. Both isotopes degrade with time and must be replaced, otherwise the it becomes less of a fusion bomb and more of a fission bomb. (The fission bomb actually initiates the fusion reaction that increases the bomb's yield by an order of magnitude or two...or three.)The electronics in the bombs would also be upgraded, increasing the reliability of the PALs (Permissive Action Links) and the fuzing of the bomb.
In the long run, it's a cheap and long overdue upgrade.