Lutzow vs. US heavy cruiser

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tommy303
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Re: Lutzow vs. US heavy cruiser

Post by tommy303 »

Depending on the fuze, whether Mk11 or Mk21 Mod 0, a percentage of shells whose fuzes functioned properly still might have passed through the ship at such close ranges. The standard delay element in both had a nominal burn time of .035 second, while the functioning time of the fuze, that is the time it took for the mechanical movement of the various parts to fire the delay element was another .003 seconds; thusly the delay time was quite long at about .038 seconds.

With the MK11, the time would have been slightly longer since fuze initiation did not occur at impact but after initial impact. In this fuze, the impact threw the inertial slug forward against a coil spring, in effect cocking the mechanism and holding the slug there by deceleration; when the shell pulled free of the armour or whatever stout structure retarded its progress, the lessening deceleration allowed the spring to throw the slug backwards again, bringing the lead-in and lead-out flash holes into alignment (thus finishing arming) and at the same time throwing the primer down onto the firing pin. This in turn set off the detonator which fired the delay. The mechanism of this fuze though, was easily jammed at moderate to high oblique impacts, ricochets or if the shell exited the plate seriously yawed.

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Re: Lutzow vs. US heavy cruiser

Post by Dave Saxton »

It would appear that the British use of nominal delay times of 0.025 seconds wasn't really unwise. This shorter delay time is more useful against a wider variety of harder and relatively softer targets, and over a wider variety of battle ranges.
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Re: Lutzow vs. US heavy cruiser

Post by tommy303 »

This shorter delay time is more useful against a wider variety of harder and relatively softer targets, and over a wider variety of battle ranges.
FIguring in the .003-second inherent delay caused by all the parts that need to move to initiate the fuze, overall delay would have been .028-second in British fuzes when set to delay. Pyrotechnic delays though, are not always precise as they are affected by a number of factors including humidity and barometric pressure. Variations in delay are usually longer rather than shorter though. British base fuzes for non fixed rounds usually had a cut off screw which could be adjusted to set the fuze for either delay or non delay depending on what the target was.

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