Is there any atomic bombs that where preserved from world war 2?

There are atomic bomb casings that remain from the 1945 to 1948 period, but most (if not all) were probably built postwar. There were only four functional atomic bombs actually built prior to the end of the war and three of those were detonated (gadget, little boy, fatman), leaving only one (unnamed) actual World War 2 atomic bomb remaining after the war. This bomb was either detonated later in one of the nuclear test shots or its special nuclear materials were recycled to make newer more efficient/safer atomic bombs by 1949. Also the conventional explosives used in the explosive lenses of world war 2 implosion type atomic bombs (composition b, baratol) are much too unstable for use in weapons intended for long term stockpiling.

Several museums preserve atomic bomb casings, a few are:

• Bradbury Science Museum, Los Alamos, NM
• National Museum of Nuclear Science and History, Albuquerque, NM
• Navy Museum, Washington, D.C.
• West Point Museum, West Point, NY
• Trinity Test Site, south entrance via Alamogordo, NM tularosa gate, north entrance via stallion gate (only open 2 days a year, only fatman style casing)
• etc.

It is important to realize that when Los Alamos built the early atomic bombs they were not delivered to the field assembled and ready to use, instead they came as a kit of parts requiring final assembly in the field. For example a MK-III (e.g. fatman, the unnamed bomb) arrived in two heavy wooden crates and the plutonium was shipped separate from those crates. It took 3 days of work to perform final assembly of a MK-IIIin the field, if the bomb could not be used immediately then every 3 days the lead acid battery that powered the bomb's electronics had to be recharged until on the 9th day after assembly, when the bomb had to be completely disassembled (which took 3 more days) and the parts returned to their crates so the lead acid battery could be replaced when the bomb was reassembled at a later date. The neutron source used in world war 2 atomic bombs (and almost all atomic bombs built before about 1955) used polonium-210, and had to be removed and replaced every 138 days or the bomb might not explode when desired. The world war 2 atomic bombs were very inconvenient to use and the US Military was very anxious to see them all replaced with newer models that were simpler to use.

Another thing to be aware of is that not all apparent "fatman" casings exhibited in museums are really atomic bomb casings, some are pumpkin bomb casings (a pumpkin bomb was a large conventional blockbuster bomb used for practice drops by atomic bomb crews, several were dropped on Japan prior to the actual atomic bombings, they weighed the same and had the same size and shape as a real MK-III), and others are mockups built specifically for the exhibit.

In 2003 I visited several museums with atomic bomb casings, that year none of them had little boy on exhibit. I found out why in one museum where they had replaced the little boycasing in the exhibit with a sign that stated all of them had been removed from museum exhibits to be modified to remove one external feature still classified top secret!!! So even if it is a real period casing, it may not appear as it did originally as parts may have been removed or modified for security or other reasons.