WASHINGTON  Instead of sending helicopter batteries, the United States shipped four electrical fuses for Minuteman nuclear missile warheads to Taiwan, a mistake that was discovered only last week  a year and a half after the erroneous shipment, Pentagon officials disclosed on Tuesday.

Officials said the nose-cone fuses contained no nuclear material, and were similar in function to the ones used for conventional munitions, although these were designed specifically to send an electrical signal to the trigger of the MK-12 nuclear warhead as it was approaching the ground.

Even so, the incident is another embarrassment for America’s nuclear weapons establishment, in particular the Air Force, which previously disclosed that a B-52 bomber mistakenly carried six nuclear cruise missiles on a flight from North Dakota to Louisiana last year.

The United States government is one of the most relentless advocates of halting the proliferation of nuclear weapons, their components and the ballistic missiles to carry them, and has made public cases against potential adversaries like North Korea and Iran. It has even criticized partners like Russia for not sufficiently safeguarding its stockpile of weapons.