"Mycroft" wrote in message
...
If you watch the 1953? film it pretty much explains the reasoning behind
the
bomb, the torpedo nets plus they needed a minimum of 5000lb of high
explosives to have a chance of breaching the dams. In an interview given
by
Wallace he stated that his famous 10 & 5 ton "Grandslam" an Tallboy bombs
were originally considered but would only work with a direct hit, any sort
of near miss would do no damge because of the water cushioning effect.

IIRC, the Paul Brickhill book mentions the 12,000 lb Tallboy being used
against the dam at Kembs in Germany; afraid that the sluice gates would be
opened and flood the area of the Allied advance, the powers that be
despatched 617 Sqn to drain the reservoir first. The bombs were dropped from
low level with delayed fuses and succeeded in destroying the sluice gates,
for the loss of two aircraft.

Jon.