During the cold war a lot of nukes wes routinely strapped to planes and flown around for no other good reason than saber-rattling. And that was how they kept the world safe.
And it can be argued that it worked very well.
Naturally accidents happened at times, for us here in Denmark the B-52 crash at Thule AFB is the most well known, but in that particular accident most of the radioactive material was recovered (or so they say), just as in most of the other accidents they had.
Not so for the H-bomb lost off the coast of Tybee Island, Georgia, USA:
On the night of February 5, 1958 a B-47 Stratojet bomber carrying a hydrogen bomb on a night training flight off the Georgia coast collided with an F-86 Saberjet fighter at 36,000 feet. The collision destroyed the fighter and severely damaged a wing of the bomber, leaving one of its engines partially dislodged. The bomber's pilot, Maj. Howard Richardson, was instructed to jettison the H-bomb before attempting a landing. Richardson dropped the bomb into the shallow waters of Warsaw Sound, near the mouth of the Savannah River, a few miles from the city of Tybee Island, where he believed the bomb would be swiftly recovered.
It's still there. Of course the accident was covered up, but recently documents with some details was declassified.