The picture is of a US Model 1917-18 Knuckle "knife".
Early in WWI, the military realized they would need a fighting knife for use in trench warfare, so the hardware firm of Henry Disston & Sons was given the job of developing a suitable weapon.
The Disston knife is actually more of an "ice pick" bladed stabbing implement.
The triangular blade was 9 3/4" long, with a black finish.
The handle was walnut with shallow finger grooves.
The knuckle guard was formed of stamped steel with pressed out pyramid shaped points.
There was a conical staked nut holding the blade in the handle, and this could be used as a "skull cracker".
The scabbard was made of green tubular leather with a blackened steel tip and throat, with a standard wire pistol belt hook.
The scabbards were made by the Jewel Belt Co.
There was a second type, or version, often known as the 1918 model.
The only difference was, instead of having a row of pyramid shaped points running down the middle of the knuckle bow, the outer edges of the knuckle bow were formed into a double row of triangular, flange-like "teeth" which were folded down to form a double row of striking teeth.
The Model 1917/18 was made by the following companies:
Henry Diston & Sons-- HD&S
Onida Community Limited-- O.C.L.
Landers, Frary, & Clark-- L.F. & C.
American Cutlery Co.-- A.C. Co.
After WWI, the Model 1917/18 was declared surplus and all remaining knives were sold as surplus during the 1920's.
In WWII, these surplus knives were dug out of footlockers and collections and given to soldiers heading overseas, so you occasionally find one having been used by a WWII vet.
Although they were no longer GI issue, and none were known to have remained in government warehouses past the 1920's, 1917/18 knives were used by knife crazy soldiers.
Immediately after being issued and used in combat, deficiencies in the 1917/18 were found.
First and most important, the 1917/18 WASN'T a knife.
It couldn't be used to cut or slice, and as such was useless as a combat knife.
Since a soldier needed a tool as well as a weapon for slicing rations, cutting rope, and all the other uses a soldier needed an edged tool for, he also needed to be issued with an actual knife.
This meant that a soldier would be carrying a long 16" bayonet, a 1917/18 fighting knife, and would still need a real knife.
The second problem was, the 1917/18 was a long, bulky weapon, that was easy to get fouled with other equipment.
Due to the shape of the steel throat of the scabbard, the knife only fit the scabbard one way, and wasn't usable with the left hand since the handle would stick out if the knife was sheathed on the left side.
Last, the 1917/18 was not usable as a slashing weapon like a knife could.
To correct the problems with the 1917/18, in 1918, Major Eugene McNary of the AEF designed and had patented a new trench warfare weapon.
This was the famous Mark One, 1918 trench knife.
Incorrectly known as the "1918 Brass Knuckle" knife, this was actually the US Mark One.
The Mark One was a true knife, with a 6 3/4" double edged dagger blade.
The handle was actually made of cast bronze, which used a conical steel nut to hold the blade in.
The Mark One's blade was blackened with a gun blue type finish, the bronze handle was chemically blackened, with spikes formed on each knuckle bow.
These spikes were intended to prevent an opponent from grabbing the knife hand, as well as to improve the striking power.
The Mark One was made by Landers, Frary, & Clark, Henry Diston & Sons, and a VERY few by Onida Community, Ldt.
The Mark One scabbard was made of two halves of steel, joined by a rolled bead-type edge.
There were a double row of slots, top and bottom, front and rear, that served to hold the blade in the scabbard and prevent rattling.
The scabbard was first copper plated to prevent rust, then chemically blackened.
All scabbards were made by L,F, & C.
On the scabbard body were two prongs that were to be slipped over the cartridge belt, the upper prong being bent upward slightly so it could be slipped UP through the top grommet of the standard cartridge belt, and the lower prong over the belt.
These prongs were attached to the scabbard by copper rivets.
It was these prongs that were the weakness of the scabbard.
When an attempt was made to bend the upper prong so it could be fitted to the the narrower pistol belt, the prongs would break off.
Also, most soldiers attached the scabbard to the outside of the belt and any jerk or pull on the scabbard would break the prongs off.
Apparently, the scabbard was intended to be mounted on the INSIDE of the belt.
Knowing that it would be sometime before American manufacturers would be able to supply Mark One knives, Major McNary contracted with a French company to make a version of the Mark One in France.
This is the "Au lion" version of the Mark One, so called for the brand name and a stamped logo of a reclining lion on the blade.
The Au Lion was very similar to the US Mark One, but the blade was was the same as used on a French fighting knife, and the handle was made of true brass.
The blade and the handle were left unfinished and bright.
The French version handle is noticeably different with a different shape to the knuckles, lacking the spikes of the American version, and being of much poorer quality.
The Au lion scabbard is a European type tubular steel scabbard with the two prongs welded on the back.
It's suspected that the American made Mark One didn't arrive in France in time to actually see combat.
After WWI, some Mark One knives were declared surplus and were often given away as free gifts to good customers by sporting goods companies, usually as a gag "anti-bear" weapon.
These usually have an advertising message stamped on the reverse side of the handle.
During WWII, the Mark One was the only fighting knife available, and it was heavily issued to early paratrooper and Ranger units.
It was the scabbard prongs that were the problem, and as they broke off in heavy use, expedient scabbards were used, usually whatever leather scabbard could be found.
Realizing that the Mark One's bronze handle was a critical war material, when the supply of Mark One's quickly ran out, a new US fighting knife was developed.
This was the US M3.
This leather handled knife was the standard fighting knife of WWII, and was used as the pattern for all US bayonets from the M1 Carbine to the M16
The Model 1917/18 trench knife often shows up for sale, and Ebay is a major source for them.
Doing an Ebay search under "Trench Knife" will usually show several for sale, both with and without the scabbard.
Doing a search using the completed auction option will show what knives have sold for.
The 1917/18 is plentiful enough, that one company is making an exact replica of the original Jewel Belt Company scabbard.
The Mark One is more popular and rare, and prices tend to be quite high, especially for one that has an original steel scabbard.
Prices are even higher for versions with scabbards with both prongs intact.