About the M3 Trench Knife in general...
It was first used in World War 2 (developed in 1943) and most of the guys who had them wore them strapped to their thigh. Issued to everybody who didn't get a bayonet. It has a 6-3/4" carbon steel blade with a 3-1/2" swedge; it was ground, but not sharpened. It was up to each individual soldier if he wanted to sharpen it or not. The handle was made of copressed, stakced leather. The guard and pommel were made of carbon steel. Overall length was 11-3/4".
The M3 was very similar to the M4 bayonet used on the M1 Carbine. The M-3 can be distinguished from the M-4 bayonet by the straight guard on the bayonet vs. the angle in the M3 guard. The bayonet guard has a hole for the M-1 Carbine muzzle; the M3 doesn't.
The M3 was manufactured by a total of nine vendors:
Aerial (Aerial Cutlery Mfg. Co.), Boker (H. Boker & Co.), Camillus (Camillus Cutlery Co.), Case (W.R. Case & Sons), Imperial (Imperial Knife Co.), Kinfolks (Kinfolks Inc.), Pal (Pal Blade & Tool Co.), Robeson (Robeson Cutlery Co.), and Utica (Utica Cutlery Co.)
The metal parts of early M3s were blued, then replaced by the Parkerized finish seen on most M3s.
The original sheath for the M3 was the leather M6, developed with the knife in 1943. The M6 had a body made of two pieces of leather riveted together, with a metal shield near the bottom. There is a snap loop to hold the knife handle. The leather is doubled over and riveted at top to hold an M-1910 belt hook. M6 sheaths were often cut down to eliminate the metal hook at the top which interfered with strapping it to the leg, paratrooper style.
Within a year, the leather sheath was replaced by the M8 or M8A1 olive drab fiberglass body with steel throat.
About Boker's M3 Trench Knife...
They're reproductions (same specs as the originals) and are of nice quality. The knives themselves are made in China and are serialized on the guard. The sheaths are made in Germany. I know that "China" stamp will turn some people off, but it's a very high-quality knife. If you weren't told it was China-made, you wouldn't know. Not bad for the $60 they're available for..
For what it's worth, Ontario makes an M3 Trench knife as well. It costs about $50 and comes with a leather (not the M8) sheath...
Also, notice the slight bend in the guard; in one photo (the Boker), it's on the top of the blade (the spine) and on the Ontario photo, the bend is on the cutting edge half. In the originals, the bend was at the top (like the Boker photo).
I like the M3 Trench knife so much that I had one of the originals tattooed on me...
