A trench knife is a like a combination between brass knuckles and a fixed blade knife. This type of knife has been around for quite a while, but it’s only recently that something like this comes along:
Watch a video demo of it here.
It takes the classic trench knife a step further by adding in an assisted opening mechanism. It’s not a switchblade, though, because a button isn’t pushed to deploy the blade. Instead, a part of the blade itself is manipulated, which in this case is a tab you can see in the video.
I’ve only seen this particular knife available at KnifeDepot.com, where it’s simply called the Solid Black Spring Assist Knife with Knuckle Guard. I saw it while researching something else and thought someone out there should stick it in a story. It has fiction written all over it.
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The Writer’s Guide to Weapons: A Practical Reference for Using Firearms and Knives in Fiction (Writer’s Digest Books) comes with everything but the ammo. Pick up a print or digital copy from these fine retailers: