If we're talking about "greatest ever blunders" I'd like to nominate the decision to take the Fairey Battle of its day, the Tornado, and turn it into an air defence aircraft. The second biggest blunder was committed by the highly-paid light blue help who accepted the wretched thing into service - OBEs and Knighthoods all round, hoorah!
Ali,
Out of interest, hindsight etc blah, but was that believed to be the case at the time? If there was a messageboard like this around then, I wonder what it would have said.