Type 3rd year Time/Impact Artillery Fuze.

By Patrick Phillips

Developed in 1914 (the third year of emperor Taisho’s reign), the type 3 artillery fuze is one of the least documented pieces of Japanese ordnance. It is a combination of time delay and impact fuse used for a variety of purposes. The type 3 owes its origins to the British No. 80 time/percussion fuse, which itself, is a close copy of the German Krupp-designed M1903. The type 3 was primarily employed for use on the 75mm shrapnel shell, fired from the type 94 mountain gun, and later used in the type 41 mountain gun. This shell essentially acted as a sort of canister shot. The inside of the steel shell would be filled with steel or lead shot embedded in a resin matrix. At the base of the shell was a detonating charge. The fuze would ignite a powder train that would travel through a central ignition tube, through the shot,

and to the bottom of the detonating base. The base would explode and launch the shot as a sort of giant shotgun.

Figure 1: Illustration showing the shrapnel shell concept. Note the bursting charge at the base of the shell, propelling the shot forwards.

In order to achieve this effect, the fuse could be set to a calibrated time delay system, so as to detonate the shell after a certain number of seconds. The type 3 fuze could be set to detonate anywhere between 0 and 22 seconds. When set to 0, the shell detonates almost immediately once it leaves the gun bore. This would have been used in close fighting, and against cavalry charges. The fuze can also be set to detonate on impact only and act as a high explosive fragmentation shell. If set in time delay, the fuze will detonate if the shell impacts a surface before the time delay can detonate it.

Figure 2: US intelligence illustration of the internal workings of the type 3 fuze.

The type 3 fuze body is made of a single piece of brass with a spindle in the center. The upper and lower sections of the spindle are hollow and divided by a center firing pin. The firing pin is double-ended and serves to ignite the time delay upon set-back and to detonate the shell on impact. Two time delay rings, each containing a black powder train, fit over the spindle. The lower ring is moveable and used to select the amount of time delay. It has time graduations in 1/5 of a second graduations from 0 to 22 seconds. Impact mode is selected by rotating the lower band past 22 seconds to a single large line. The upper ring does not rotate and is held in place by a brass pin that can be removed for disassembly. Above the time delay rings are two steel washers, each having a slightly “dished” shape. These serve to provide compression force to lock the lower time delay ring in place once the nose cap is tightened down on top of them. In the upper hollow portion of the spindle are several gas vent holes around the perimeter. Above these are the four-fingered arming sleeve, and time delay initiator. The upper end of the spindle is threaded to accept the nose cap, which is tightened down and secured in place by a set screw. The nose cap is stamped with manufacturer and date information and has holes for a safety pin at the very top.

Figure 3: The brass pin can be removed for disassembly. Don't lose it!

Figure 4: Creep spring, foil disk, and brass plug.

The bottom portion of the fuze body contains the impact components, as well as the final black powder charge for the time delay system. In the center are the impact primer, and anti-creep spring. The impact primer is held in the rear position by two spring-loaded detents. These detents retract under centrifugal force, allowing the impact primer to move forward against the creep spring and strike the impact primer when the shell hits a surface. These are both held in place by a lower threaded plug which has an opening in the center to allow for the priming compound to ignite the black powder charge. This center opening is covered by a foil disk to keep the black powder from interfering with any moving components. The base of the fuze would then be filled with a black powder bursting charge and then capped with a threaded brass disk to close the lower assembly.

Figure 5: The lower fuse assembly is completed by inserting its components and installing the brass plug. This cavity would then be filled with black powder and closed off with a brass cap.

Figure 6: Bottom of the upper time delay ring showing the black powder channel. The lower ring is essentially identical.

The time delay rings each has a semi-circular channel milled into the underside. This channel is filled with a black powder time fuze. This channel has an entrance hole at one end of the channel, and an exit at the other end. The upper ring does not rotate. The lower ring can be rotated to adjust the amount of time delay. Essentially, the way this works is that the distance of time fuze is being lengthened or shortened based on the position of the lower ring. When set to 0, all the entrance and exit holes are aligned, allowing the powder to burn through both time delay rings and into the base of the fuse instantly. When the lower time delay ring is set to its maximum delay of 22 seconds, the entrance and exit holes are placed at their maximum distance apart. The upper time ring must burn around completely before entering the lower ring, then the lower ring must also burn around completely before reaching its exit hole into the base of the fuze. To set the fuze into impact mode, rotate the lower time delay ring past the 22-second mark to the next large indicator mark. This will ensure that none of the entrance or exit holes in the time delay rings will be aligned. The time delay primer will still ignite when the shell is fired and will burn the black powder train in the upper time delay ring but will not continue into the lower ring. As the shell is spun by the rifling of the gun bore, two internal spring-loaded detents will move rearward due to centrifugal force. This will allow the impact primer to travel forward, against the creep spring and detonate the shell once it strikes its target.

Figure 7: Felt and fabric washer.

I’m very fortunate to have this type 3 fuse in my collection. Not only is it almost complete (it’s only missing the internal impact primer), but it also has the original felt and fabric washers in between the different rings. These felt washers served to waterproof the fuze and keep the black powder time train contained within the delay rings. I plan on fabricating a reproduction impact primer, which should be fairly easy on the lathe.