the 'French Nail' : Field Expedience

I was recently contacted by a long ago army buddy, who was looking to have some replicas made of an early World War One object. 

Image from the Imperial War Museum

'French Nail' fighting knife ['Clous Français']

The reference he provided was from the Imperial War Museum : https://www.iwm.org.uk/collections/item/object/30003377

These were not 'regular issue' weapons, but were made at the front by blacksmiths working primarily as farriers, who's primary role was shoeing all the horses and mules used for the bulk of transport in that conflict. 

The basic raw material was supplied by converting 'screw pickets', steel posts used for holding strands of barbed wire in entanglements.

Photograph by Lt. J.W. Brooke : 1917-10-23 (IMW)

 The IWM description provides the following dimensions (of the sample pictured above) :

Depth 11 mm

Height 318 mm

Width 54 mm 

Weight 0.314 kg

As is my normal practice, I took the reference image and converted it to life size, and printed off a copy. 

My first surprise is the diameter of the round bar used. I would have expected French metric sizes at 10 mm / 3/8 inch. That 11mm is just a strange size, converting to imperial to 7/16. These knives were also made and used by both British and American troops, where I would expect 1/2 (12.5 mm) stock. Given the few clear reference images I could find of British (hence also Canadian) troops with screw pickets, I decided to use 1/2 round mild steel stock.

In use, the hand would grip inside the ring, around the blade side. The blade would point upwards from the thumb. This allows for a 'low line' stab to the gut. The heavy loop of bar thus runs over the fingers, creating a 'knuckle duster' effect for punches. The knife is primarily a stabbing tool, so the long point is more important than the cutting edges. Simple, brutal, efficient.

From the life size image, I pulled the following additional measurements :

Blade : 20 mm / 3/4 inch wide x 15 cm / 6 inches long

Handle Interior : 80 mm / 3 1/8 long x 30 mm / 1 1/8 wide

The handle interior space was a bit puzzling, being a bit on the small size. I have fairly small hands and would have found the historic sample a tight fit.

The two replicas, upper as diamond / lower as triangle (on 1/4 " grid)

As a primary thrusting weapon, the blade cross section could have been either diamond or triangle - either would produce two cutting edges. The most likely would have been a more standard diamond, but the triangle results in a thicker, and thus more rigid, central spine. None of the images or descriptions I could easily find via the internet specified which. As a forging test, I decide to make one of each cross section. The one closest to the reference sample (smaller hand grip) as diamond. The second replica was made with an intentionally larger interior grip size to fit a more modern physical build, and I used a triangle cross section. I was a bit surprised to find the forging steps required for either turned out to be pretty much the same. The diamond needed forging on four sides, but the triangle I found needed more control with the hammer blows (although admittedly not a shape I make that often).

I also made some trials working 1/2 round into a triangle bottom die. The die I had on hand was more of an equilateral triangle, so not ideal for the wider final shape required. With the proper shaped die made up, the time to forge the triangle cross section would be greatly reduced, and the forging would produce both a significant central spine as well as thinner cutting edges. This most certainly would speed the work if a smith had a large number of requests for this knife. (Worth noting that the sample does not show the more exaggerated cross section suggested by the test pieces I made.)