Nice. All British tanks.
For a time, I worked at a military fan and impeller manufacturer in Sunbury, Airscrew Howden (I wonder if they're still around?). My job was testing various aspects of electric and hydraulic fans. Once a week, I had to test the (hydraulic powered) fans that cool the engines in the Challenger II tank.
This is a bank of two fans approximately 3/4 of a metre across each. In application they spin at up to 2800rpm if memory serves me correctly, and at that speed they produce a lot of noise. The main test we were required to perform was for impeller integrity, because as you can imagine, if a fan blade a square foot in area and a centimetre thick comes off at 2800rpm, we're going to ave a scenario for the crew, somewhat similar to putting a spider in a jar of nails and shaking it.
So, we put them up on hydraulic rigs in soundproof chambers, and spun them up to 5800rpm for 15 minutes. This noise could be heard a mile away, from a soundproof room. I never had any failures, thank god (it was dangerous for us as testers, too, naturally), but a colleague did, and one of the blades came flying off, went through one soundproof wall, through the walls of the next booth and through both walls of a third booth, before embedding in the wall of the fourth.
It was nucking futs I tell ya.