Work is done; see first post, these are available with alpha channels, though currently not up on the mod section.
These are based right off photos of U-boots before the onset of hostilities.
Clearly it's from Koch's Fraktur typeface, but I've not been able to find one that matches it, hence making my own. Why doesn't it match? Likely artist/painter's winged it when painting and then settled on a standard.
Also bear in mind that no two numbers were exactly the same at the time, each had subtle differences (from comparing photos), so I've tried to form some scaling and ratio standards, this was a crude first draft, so as I clean it up and make things more uniform; it'll change.
See original post on getting the numbers with alpha channels.