This is a very unique piece, a veteran bring-back.  It consists of a Japanese Navy Dagger hilt to which has been fitted a Sankaku yari (三角槍, "triangle spear").  It has a very thick blade with a sharp point.  The piece resembles a 3-edged narrow spike (think a triangular cross-section).  The spear tip was best suited for penetrating armor, even armor made of metal, which a standard yari was not as suited to.  There is considerable rust, but given the thickness of the piece, it could be beautifully restored.  This piece was inspected personally by Japanese sword expert Mike Yamashita.  He indicated that spear tips like this were used from the 1500s to 1800s, but the writing on the tang dates this in the 1500s.  He also commented that he has heard of pieces assembled during WWII from family blades to be carried as combat fighting knives, but this was the first one he has ever seen.  I disassembled this piece, and have photographed the writing on the tag.  If anybody can help further with this, it would be greatly appreciated.  Very interesting piece!