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UMNP-1 is a booby trap fuze designed to initiate mines and demolition charges by either pressure or tripwire actuation.
A hollow spring-loaded striker is held back by retaining balls which, in turn, are held in position against the walls of the fuze body by a central plug.
In the end of the fuze body, a piston bears on an actuating rod which runs down the centre of the fuze body to the plug.
In contact with the piston is a spigot, which is fitted with four pressure prongs; there is also a ring for the attachment of tripwires.
A safety pin runs through the spigot, secured by thin lockwire, preventing movement until the fuze has been set up.
The fuze body has a male M10 × 1 thread and is fitted with a stab-sensitive detonator assembly, which is sealed into position.
The metallic fuze body is unpainted and without markings; the prongs may be either metal or plastic.

Once the fuze has been screwed into the parent mine or demolition block, one or more tripwires may be attached to the ring before the safety pin is removed to arm the assembly.
Sufficient pressure on one of the prongs or radial pull on a tripwire tilts the spigot, which cams the piston down into the tubular fuze body.
The movement is transferred to the central actuating rod which pushes the plug forward; this allows space for the retaining balls to move in, releasing the striker onto the stab-sensitive detonator assembly.
Direct (axial) pressure will also initiate the fuze.

All photos © Josip.


Practice version, UNMP-1V :

same fuze but made to be re-used.


Shown on the right are two UMNP-1V pressure fuzes with different lengths and threads.
According to Josip, this difference is made to fit another type of percussion cap. The mechanisms stayed exactly the same.

Left type : Length 56,3mm
Right type : Length 51mm

Diameter : 11mm

Photo © Gilles.

Box of UMNP-1V

Shown on the right and below is a full box of the UMNP-1V, which is the training version of the UMNP-1.
Hence the yellow diagonal stripe on the box, this also indicates that the contents is for training purposes.

Photos © M. Jochoms