Unidentified US Combination Firing Device

Unidentified US Combination Firing Device (inert) seems to be in the same family as M6 and M7 but it’s not an M5 and certainly not a variant of an M1 (although both the M1 and the unidentified one do share the same mix of short and long threaded ends as well as the vented ones seen in photos.) It also shares the same cotter pin hole position as the M1. The unidentified one also seems to have an inherent design problem --top buttons fall off

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I never saw one of these in the Army. What is their purpose? Interesting looking gadget, enough to make me curious about what they were used for.

Thanks for posting.

John Moss

Unfortunately they’re screwed into grenades for use as booby traps. The ones I illustrated in the photos are combination fuzes. They allow grenades to be used as pressure sensitive anti-personnel mines AND also with pull-type trip wires. Their are others still that work with release-type trip wires, so that the device fires the grenade when you let up on the wire. I am glad to hear that you never saw them while you were in the army. These booby trap fuzes have problems as you can see by the warning on the tag, and of course the booby traps themselves know no distinction between friend or foe. John

Basically these are mine fuzes to be used on designated mines and a whole row of ordnance items the standard thread of the coupler fits.

The one on the far right apears to be a Combination Fuse M6/M7:

Here it is attached to a grenade:

The three on the left look to me to be a modified M6/M7 to a Pull/Release igniter, perhaps an early version of the Igniter Time Blasting Fuse M60, to touch off a fuse leading to TNT or det cord.

As to the two fuses at the top, the longer fuse goes into a standard grenade for timed ignition, the shorter fuse is for immediate ignition.
They were used well into Korea, and in the early days of VietNam. Some were still in use with certain… groups… into the early~mid 80s’. I would presume there was a large stockpile available, and convenient, when you did not want the ‘other guys’ to know who had been in the neighbourhood. Ah, fun days.

This may help, I was off a littel bit on the left hand items:
Combination Fuze M6, (left), and Combination Firing Device M1, (right).
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Combination Fuzes M6 and M7
General: The combination fuzes M6 and M7 are designed for firing explosive charges either by means of a trip wire or by pressure. The mechanical construction of the fuzes is similar, but they differ in the loading of the base plug.
The M6 is 6.6 inches in length, and the threaded portion of the base is ½ inch long; the M7 is 7.13 inches in length, and the threaded portion of the base is ¼ inch long. The igniter charge of the Combination Fuze M6 consists of 10 grains of black powder, while the detonator of the M7 consists of a U.S. Army Special, Type A, blasting cap.
Description: The fuze consists of a head and case crimped together, which contain a trigger pin, a release pin, and a firing pin, each with a spring. A small groove in the firing pin is held in the narrow part of a keyhole slot in the release pin, the release pin being provided with a ring for attaching trip wires. The trigger pin has three one-inch-long prongs of stiff steel wire projecting from its head. A wedge is provided on the bottom of the trigger pin which enters a slot in the release pin. When sufficient pressure is applied to one or more prongs, the release pin is moved aside and the firing pin passes through the large opening of the keyhole slot. Two safety pins are provided, one passing through the firing pin and the other passing through the release pin. The base is a hollow cylinder which contains the primer
Use: The Combination Fuze M6 can be used in the Anti-Personnel Mines M2A1, M2A2, M2A3, or M2A3B2. The Combination Fuze M7 is used in the Anti-Personnel Min M3.
Operation: When the fuze is armed, either a pull on the release-pin ring of 6 to 10 pounds or a pressure of 10 to 20 pounds on the three prongs (10 to 30 pound on one prong), depressing the trigger pin 9/32 inch, will move the release pin 3/32 inch, so that the larger hole is in line with the firing pin. The firing pin is thereby released, and the compressed firing-pin spring will drive the striker down on the percussion cap.
Remarks: The Combination Fuzes M6 and M7 replaced the Combination Fuzes M2, M2A1, M3, and M3A1 in the Anti-Personnel Mines M2 and M3 Series.”