This knife was originally purchased by a collector from Frank Trzaska.  Here is Frank's description of this knife:

On page 190 of MILITARY KNIVES, A REFERANCE BOOK, "For the lack of a better name I'll call this knife the RVN 1918 Mk2, as it consists of parts from both the 1918 Mark 1 Trench Knife and the Mark 2 USMC Fighting Utility Knife. This knife was the brainchild of a select group of the 5th Special forces members. While the first knife was produced as a weapon for actual use, the following knives were produced strictly for trade purposes." I purchased this knife in 2008. Most of these hard to find knives have found their way into the hands of serious collectors and rarely come up for sale. Two things make this knife slightly different from the few others that were made. First the backside of the guard is usually cut away so that the knife can lay flat on the sheath. The guard on this handle was not altered. Instead the sheath was molded to fit the larger guard. The second difference is that the blades on most of these special forces trade knives were Mark 2 blades. This one was made from what must have been a new Pal RH 36 blade. It still has all its original Parkerizing. The sheath was made for this knife and has the attachment for the US pistol belt. This is a very rare piece. Don't miss this opportunity.

This US Vietnam RVN 1918 Mk2 5th Special Forces trade fighting knife and its scabbard are in excellent condition.