In case this hasn't been mentioned before ....

One of the problems that engineers have, when building certain types of sensitive instrument for use in deep space, is finding steel which was smelted before 1945: any steel smelted after The Bomb was first dropped will be sufficiently radioactive to ruin the sensitivity. The major source of "clean" steel, I read once, is the ships of the German fleet that were scuppered in Scapa Flow in 1918.

Now I'm wondering whether these Nazi-scuppered ships could be a similar source of clean steel. Cue an entire generation of archaeologists going spare.