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  1. #11
    Premium Member
    Join Date
    May 2015
    Southend on Sea
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    Tins for Percussion Cap Mk III & Fuze Percussion Bolt.

    The rimmed snouts were the first generation and were used with Igniter Safety Fuze Percussion (ISFP). ISFPs were widely used by the Royal Engineers (RE) as a means of initiating Safety Fuze. When used in this role they were expected to remove the used snout and replace it with a fresh one which were issued separately in the tins shown. Obviously if they were used in booby traps this was not feasible.
    ISFPs were used by RE in some of their own Anti-Tank Mines which were held by them and not RAOC. They were also used in RE improvised A/Tk mines, which they made up with any explosives they could lay their hands on.

    ISFPs were also used as the basis of Switches No 1 Pull and No2 Pressure. Switch No 3 only used the rimmed snout (see photo). The SOE photos are fairly indistinct. See photo showing the Switch No 3 striker pivoted out of the way to allow insertion of the rimmed snout. The other photo shows the tip of the striker which would help to keep the snout in position.

    Eventually they were produced in numbers and became throwaway. The ISFP package photo refers to 1 and 2 which are probably for snouts. The actual package contains 20 x 10 tins of complete ISFPs. These tins had a Scored Tear Off strip (like a corned beef tin). Apparently over 350,000 were made in the 1950s, without the screw cap at the striker end.
    There is also a watertight version of something very similar.

    I include a photo of a Switch No 4 Pull, which shows the screwed snout. This was also used in Switches No 5 Pressure and 6 Release as well as the Time Pencils and 'L' Delay.

    Despite the introduction of the Switch No 4 Pull, the RE continued to use the ISFP. For their purposes it is likely that the pin being pulled at right angle to the body enabled them to vary the strength of pull required and anchor it easily. I know from personal experience that the length of travel of the claw and Switch No 4 ball ended striker and the relative strength required to pull it against the already compressed spring, is considerable. The RE are laying mines and traps under the noses of the enemy and would need to be able to anchor the item easily which is difficult with the axial pull on a Switch No 4.

    ISFP Mk III - description - 1.jpgISFP Mk III - package - 1.jpgISFP Mk III - rimmed snout - 1.jpgSwitch No 3 Release - 1.jpgSwitch No 3 Release - striker pivoted to allow rimmed snout - 1.jpgSwitch No 4 - Pull screwed snout - 1.jpg
    Last edited by AE501; 11th June 2018 at 06:32 PM.

  2. The Following 3 Users Say Thank You to AE501 For This Useful Post:

    millsbomber (11th June 2018), ron3350 (11th June 2018), TimG (12th June 2018)


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