According to a Department of Defense report, there have been at least 32 “accidents involving nuclear weapons.” And the report only counts US accidents which occurred before 1980.
What kind of accidents you ask? Well:
They include such gaffes as nuclear bombs inadvertently falling through bomb bay doors; the accidental firing of a retrorocket on an ICBM; the vast dispersal of radioactive debris; and the loss of enriched fissile material and nuclear bombs (which are “still out there somewhere”).
I’m sure after each of these accidents the only words uttered were, “Oops.” Read the entire report here (It’s a PDF document so be warned).