Nuclear weapons systems are composed of the weapon (bomb or warhead), the delivery device, and the guidance system. Nuclear weapons include both "atomic" (uranium, etc.) and "nuclear" (hydrogen) bombs. Hydrogen bombs are thousands of times more powerful than the Hiroshima-type atomic bomb. The development of nuclear weapons started with atomic bombs and shifted to nuclear weapons.
*Strategic nuclear weapons and theater/tactical nuclear weapons
Nuclear weapons are broadly classified as strategic weapons or theater/tactical weapons. In general, those that produce the largest explosions are strategic weapons, and those that produce smaller explosions are theater and tactical weapons. However, this distinction does not always hold. The chief distinction is the nature of the delivery device. Weapons loaded on intercontinental ballistic missiles (ICBMs), submarine-launched ballistic missiles (SLBMs), and strategic bombers that can directly attack the enemy's homeland are all considered strategic nuclear weapons.
Weapons loaded on intermediate-range ballistic missiles (IRBM), which target areas other than the homeland, medium-range ballistic missiles (MRBM), and intermediate-range bombers are theater nuclear weapons. Weapons loaded on short-range ballistic missiles (SRMB) are tactical nuclear weapons. These weapons are quite varied: nuclear bombs loaded on fighters; air-to-land, air-to-air, and land-to-air missiles; army and navy artillery-fired atomic projectiles; nuclear torpedoes; nuclear depth charges; and nuclear land missiles. They are deployed along with conventional weapons in every field of weaponry. Nuclear land mines, artillery-fired atomic projectiles, SRBMs, etc. are sometimes called "battlefield nuclear weapons."
*Miniaturized nuclear weapons and neutron bombs
A striking development in nuclear weapons since the 1960s is their rapidly shrinking size. One example is the neutron bomb, which was highlighted during the Reagan administration. Officially called a "radiation-reinforced warhead," this anti-personnel weapon is designed to generate a low level thermal ray and blast, but to kill the enemy with a huge emission of neutron radiation.
Future nuclear development will be characterized by continued reduction in weapon size. Sub-critical nuclear testing is linked to the development of nuclear weapons of less than one kiloton, and even "mini-nukes" and "micro-nukes" of less than 10-100 ton.