I recently acquired a short blade in what appears to be some sort of military mount. The rust on the Nakago is extremely dark and the habaki seems very intricate. The tsuba is a single piece of undecorated iron, and the metal fittings on the handle (sorry, I don't know the terminology) seem much, much older than the handle itself. There are mei on the ura and omote sides of the nakago, slightly interrupted by a second mekugi-ana that seems to be from a re-mounting. The hamon can't be seen in the photos, but in the right light, is very intricate, with unattached inclusions which don't connect to the rest of the hamon.
The saya is plain wood with a leather sheath.
Any help with identifying the smith, date, or even the style of the sword would be a huge help. If the mei isn't legible just tell me and I'll try to find some tissue paper for a tracing.