U-99

Good observation.  I think bronze has natural properties that lend well to being constantly submerged, i.e., it doesn't rust, and it's very strong. 

Plus it looks cool, but I think that's a minor reason. 

Thanks Brumbles, really useful,

I'll post photos of the sub soon now that my computeur works once again.

Meanwhile I want to know why most ship propelers are gold like bronze?

Everything you'd ever want to know about U-boats in one semi-complete package!

http://www.uboat.net/

I had Revell's U-99 a while back.  It's a full hull version of the U-96, but with the VIIB conning tower that has the round AA platform.  It's not a terrible kit, although it's a bit lacking in detail and sharpness.  The hull is smooth with no plate detail, and the shape of the saddle tanks is a bit off as well.  Still, it's a decently large kit, and for the most part correctly proportioned.  Built out-of-the-box, makes a nice enough model, although when viewed up close, it's lack of detail shows.  If you want to do a bit of research and spend some time detailing, you can make it as nice as you please.