One of the most effective operations conducted by B-29s was the systematic mining of Japan's waterways.
Progressing through five phases and involving 1,528 sorties 13,102 mines were laid by B-29 bombers with the loss of just 15 aircraft. March 27, 1945 marked the beginning of the campaign. The 313th Bomber Wing undertook these missions, usually at night with radar, a parachute slowing the fall of each mine.
The mines rested on the sea bottom and weighed either 1,000 or 2,000 pounds, the heavier type being effective in 25 fathoms of water, the lighter one was good up to 10 fathoms.