You have to be careful, as in the comment about, oh, its a DWM...
There are many variations and navy ones are fairly rare... In the luger field, there are probably hundreds of variations, rare ones and then very common ones. You really have to know, or you'll get burned.
As an example, just because it has a 6 inch barrel, does not mean it is a navy. This one shown has the correct attributes at first glance and is probably correct (I am no navy expert), but I have seen some folks buy what they thought was correct and lost a couple of thousand on a wrong "variation"...
Ed