V-2 rocket launch failures.
Slave laborers at the Dora Concentration Camp building V2 rockets for Wernher Von Braun. More: http://www.dora.uah.edu/slavelabor.html
These photos were taken by a Nazi-sanctioned photographer for propaganda purposes (note the staging, skilled rather than manual labor, clean clothes, relatively healthy-looking prisoners), and they’re still painful to look at. I can’t imagine how horrific the reality was.
At a minimum, 20,000 laborers died constructing V-2s. At the Mittelwerk underground factory in Kohnstein, 250 laborers died per day.
An estimated 2,754 civilians were killed in London by V-2 attacks with another 6,523 injured, which is two people killed per V-2 rocket. However, this understates the potential of the V-2, since many rockets were misdirected and exploded harmlessly.