Only two nuclear weapons have ever been used: at Hiroshima and at Nagasaki. Both were low-yield weapons and used different fuels for logistics reasons: one was uranium and the other plutonium. Two is still more than enough. These were fission bombs - not neutron bombs - as the concept had not yet been developed. The neutron bomb concept was tested successfully in the late 1950s and early 1960s. The US constructed about 1000 neutron weapons during the Reagan administration. Other countries known to possess such weapons include: territories within the former USSR, China, Israel, and South Africa. It is likely that any military nuclear power with access to bomb-grade plutonium has developed these weapons at some time. South Africa has claimed their weapons were dismantled. Neutron bombs were originally fabricated using plutonium, which was difficult to acquire or produce. This limited the number of nations that could develop such weapons. However, highly effective weapons can be made from red mercury, a compound containing mercury that has been heavily irradiated. ------------------------------------------------------------ Re: "Use of nukes does not mean employment which = war use. Nuclear detonation ranges in the 1000's since the test at Trinity" I fail to see what connection this comment has to my answer, what it even refers to, or the reason this answer was downrated. The question asked if the neutron bomb has been used (no, paragraph 1) and which countries possess the technology to build them (paragraphs 2 & 3).

Many have been used by the USA but under Nevada at 1300 ft over 4000 bombs have been exploded only 2 where used in war, but many died from testing. John Wane and Yuel Brenner blamed cigarettes for their lung cancer but both were exposed to" Big Smokey" during the filming of the movie "Gengis Kanh"

Neutron bombs are very complex evolution of a hydrogen bomb. They require the minimization of blast and fallout to get the desired effects. In this they would set off a fission bomb (the smallest required for needs) to set of a fusion reaction in a suitable material surrounding this bomb. The fusion reaction produces very high amounts of neutrons that help fission any remaining fissionable material. So the bomb has to be balanced so that there is a lower enough blast to not destroy infrastructure and a high enough amount of ionizing radiation (neutrons in this case predominantly) to kill of any living organism in the desired area. Several countries are said to have them ranging from China to the US to Russia. None has been actively used for offensive purposes.