The U.S. nuclear arsenal has shrunk to less than 5,000 weapons. Most of them are warheads on ballistic missiles (1,600 on 540 land based missiles and 2,880 on 384 missiles carried on 16 submarines.) The rest are bombs or air launched cruise missiles. Tactical nuclear weapons (artillery shells, short range missiles, backpack bombs) have all been withdrawn. There are several thousand other warheads either in the process of being dismantled or held in reserve. Since 1945, the United States has assembled some 70,000 nuclear weapons. Only two have been used in combat, but another 1,054 were expended in tests. The U.S. nuclear arsenal peaked in 1967, when there were 32,500 weapons available. Production of nuclear weapons stopped in 1989. But earlier this year, the United States began building nuclear bomb components again. This was done because it was feared that the technology would be lost otherwise. It did take some effort to reassemble the technology and qualified people to make the radioactive, electronic and mechanical components needed to build a nuclear weapon. In addition to fears of losing the weapons technology, there was also the practical problem of replacing components of bombs that grow old and unreliable. The bombs are complex devices containing mechanical, explosive, chemical and electronic components that degrade over time.