Going through the Final Report by the National Commission on Deepwater Horizon. This was a mess of fail. Here I can give you a small sample of the fail:
So the blowout preventer has a final emergency solution called the blind sheer ram that would cut and seal the whole well. It would be activated from the ship or would automatically activate if connection to the ship were lost, on the assumption that a catastrophe has occurred. It had two redundant solenoids that used a 27V battery each controlled by two separate computers that ran on 9 V batteries and each connected to a coil on the solenoid. One 27V battery was dead, so the yellow side was out. Now the blue side had been wired wrong -- one coil's polarity was backward so the two coils would work in opposition when turned on. But...one of the 9 V batteries was dead -- the one hooked to the coil wired backward -- so that computer didn't run and the other computer actually ran the sheer. But the drill shaft had warped, moving it so the sheer was incomplete. Plus various other problems. Like I said, just a sample.