I have recently acquired a model U-boat, but cannot identify it exactly.

Features: No visible ballast tanks -streamlined hull

Conning tower with TWO gun platforms aft - the extreme aft platform
being lower than the other, but identical in size and shape

Gun on foredeck

Twin screws, but only 1 rudder Is this modellers licence ?)

Hand-rails on either side of conning tower


Is it a later IXD or even a modified VII ?

Any help welcome