Armor-piercing shells 1. pass through soft targets 2. delayed detonation. With WWII technology? How?

[AK84]

@KarlGauss

The bottom line seems to be that for shells of that era and type, there were delays on the order of milliseconds (6 to 13) which were set into action by (as AK84 also points out) by the shell’s deceleration (or, phrased differently, by the continued forward movement of the firing pin which allowed it to plow into the primer which then, in turn, ignited a bit of black powder aft of the primer). What I am having a hard time believing is that millisecond precision could be achieved by the chemical process of burning black powder, especially when the entire apparatus had just experienced the monumental shock of being slammed into armor at some 2000 mph! At best, I would have expected something critical to have been jiggled loose by the impact thus making it a bit of a miracle that it still fired, and an absolutely huge miracle that the powder so ignited still burned for the precise number of milliseconds originally…?

Thanks! I really do appreciate all the help everyone’s provided.

It does not need milliseconds of precision. Just needs to delay the detonation until the shell has gone through the armour belt.

[Dissonance]

@Aji_de_Gallina

Durin the Falklands War, many bombs fro Argentinian A-4s would pass through ships without going off because the fuse hadn’t been activated due to the short time the werr “flying”. I can guess a similar thing happened.

Oddly I mentioned this in another thread just the other day. The Argentineans were dropping Mk-82 retarded bombs (retarded referring to the fact that 4 fins deployed to create drag or ‘retard’ the bomb) from too low of an altitude to allow the fuse to arm. There is a propeller-like device on the nose of the bomb as can be seen in this picture here that has to complete a set number of revolutions before the fuse will arm. 13 bombs hit British ships in Bomb Alley but failed to explode due to this. They didn’t actually pass through the ships, the HMS Antelope was lost when one of two bombs embedded in the ship exploded while attempting to disarm it:

After initial damage control efforts, Antelope proceeded to more sheltered waters so that two bomb disposal technicians from the Royal Engineers could come aboard and attempt to defuse the two unexploded bombs. One of the bombs was inaccessible because of wreckage; the other had been damaged and was thought to be in a particularly dangerous condition. Three attempts by the bomb disposal team to withdraw the fuse of this bomb by remote means failed.

A fourth attempt using a small explosive charge detonated the bomb, killing Staff Sergeant James Prescott instantly and severely injuring Warrant Officer Phillips, the other member of the bomb disposal team. The ship was torn open from waterline to funnel, with the blast starting major fires in both engine rooms, which spread very quickly.

[the_diego]

Both direct contact and base (internal preset) were used by both sides. A direct contact fuze still takes time to detonate the main charge while a base fuze is preset to explode upon deceleration.

The Japanese battleships sank the gambier bay and the US destroyers mainly with 6" secondary guns. Swinging your 14"-18" guns around fast enough and pointing them below horizontal already caused enough trouble for the gunners.

[jz78817]

@TonySinclair

I think jz might be making a snarky distinction between “fuse” and “fuze.”

no, I wasn’t being snarky, I wasn’t aware that AP projectiles were also explosive. I probably shouldn’t have posted at all.

[Leo_Bloom]

We all have days like that.

[smithsb]

The internet ate my post - dammit:mad:

US military terminology:
Fuse - burning type. Like the time fuse you’d see in old western films when the mine was going to be blown up. Modern time fuse is a black powder core, fabric jacket and outer waterproof vinyl cover. No spitting flames. You can time a length pretty well. Getting a ±5 second detonation window while burning a 20 foot length of cord is easy. That’s ±5 seconds out of a total burn time of 13+ minutes. Some still used illumination mortar rounds use a length of time fuse wound in the fuse body to set the parachute/candle ejection time.

Fuze - mechanical/electronic type. A plunger or pin is driven into a detonator or delay element by impact, clockwork mechanism runout, or a charge is sent to an electric detonator caused by impact (piezoelectric) or capacitor/battery discharge.

The delay element is a manufactured pellet of black powder. The composition, grain size, and packing density is closely controlled to get an exact delay time. Typically for an artillery nose fuze, it’s .05 seconds. This gets tested at pellet manufacture, fuze acceptance, and periodically thereafter during stockpile reliability testing. Failure results in lot rejection though fully assembled fuzes may be accepted with a restriction such as “use in superquick mode only”, or “training use only”.
Jane’s has a good description - http://articles.janes.com/articles/Janes-Ammunition-Handbook/M557-PD-fuze-United-States.html

Navy base detonating fuzes use a mechanical delay in many instances. A “large” weighted plunger has to move forward to function the detonator. The travel of the plunger during deceleration provides the delay. Close tolerances also come into play. The plunger is held in the rearward positon by springs and pins locked into detents during shipment and handling for safety. The setback and spin forces during firing release the pins allowing the plunger to move forward on striking an object. A delay of .033 seconds was typical.

You could spend weeks on fuze types, mechanisms, strategies, advantages, etc… Theere is always a new type around.