I used to have a computer simulation of the Dambusters raid, which depicted the details of the approach, altitude and bomb aiming problems of the mission. To say it was difficult would be an understatement. Not only did they have to avoid enemy fire, but had to spin the bomb to get it to bounce on the water and release it at the exact moment and the exact altitude. Hell of an accomplishment.
Slide rules, Mark 1 calibrated eyeballs, coathangers and raw chutzpah.
No more difficult than bullseyeing womp rats...