My whole point about identifying the guns was to show that it must be set in the 60's due to the age of the guns, and no I'm pretty sure it's not a H&K USP, same goes with no seeing the P90 because of the period it's set in!!
Anyway, I do like the P90, shame you could use it in MGS2 or Substance, despite the fact it really is an ugly gun...looks like a black slab of steel from the side on...