The United States mistakenly sent Taiwan four fuses used to trigger nuclear warheads on ballistic missiles in late 2006 and only discovered the error last week.
Nose cone assemblies containing the fuses were recovered on Monday from Taiwan where they had been held in storage after being shipped there as helicopter batteries.
US Defence Secretary Robert Gates has ordered an investigation into the incident and a comprehensive review of the US inventory of all nuclear related components as well as of policies and procedures.
It was the second major nuclear security breach uncovered in just over six months, following the mistaken transfer of nuclear armed cruise missiles from one US base to another aboard a B-52 bomber in September.
The fuses are housed in nose cones that are fitted to the warhead of a Minuteman intercontinental ballistic missile. They are used to ignite the trigger of a Mark-12 nuclear weapon.
The sequence of errors began in March 2005 when the fuses were shipped as surplus articles from FE Warren Air Base in Wyoming to Hill Air Force Base in Utah.
Even though they were classified items they apparently were put in an unclassified logistics facility at Hill Air Force Base.
The Defence Logistics Agency then picked them out of the warehouse in autumn 2006 and shipped them to Taiwan.
The Taiwanese informed the US side that they had not received the batteries they had ordered for their helicopters, but the US thought they were talking about different sorts of batteries.
The nose cone assembly and fuse were classified but the technology dated from the 1960s.
An investigation led by Navy Admiral Kirkland Donald, the director of Navy nuclear propulsion, will determine if any secrets were compromised.
The items are understood to have been placed in storage by the Taiwanese after they received them. When the Taiwanese realized what they had, they notified the right authorities and started the recovery process.
Experts said it raised questions what else may have gone astray.
