Sommewalker, on 15 May 2012 - 05:38 PM, said:
I must beginning to suffer in old age. As I understood it a Direct Action fuze was designed to produce a surface burst. A inertia fuzed shell had a built in delay of a few microseconds as the 'hammer' ran forward onto the striker as the shell was slowed,overcoming the anti-creep spring, and initiating the explosive chain. This allowed the shell to penetrate earthworks but caused cratering. A direct action fuze operated where the striker was driven directly onto a percussion cap and commenced the explosive chain. This gave a burst (oval in shape) producing a surface blast and shrapnel effect. I am ignoring delay caused by the operation of safety devices. Obviously any type of percussion fuze had a problem on very soft going Am I now being told this is wrong? SW
Yep, that's basically right.
Pre-1914 there was no HE for 18 and 13 pr, not a lot for 4.5-in and 60-pr, and not many guns bigger than that. Shrapnel and star (and there wasn't much of the latter) needed a time fuze to burst in the air.
T&P (P being graze) P was an option to burst shrapnel behind light protection such as walls and gun shields and was considered OK for HE because it was the explosion to blow things up rather than the fragments that mattered.
One HE became prevalent (and predominant given that 18 pr was about 50/50), and fragmentation more important, then the graze as standard percussion fuzes were soon recognised as 'not the solution' because they caused too much cratering. Hence the No 106 Direct Action fuze that was the functional model for the standard fuze for decades to come. It did cause shallow craters, but nothing like graze did.
Obviously for heavy artillery, which was in the business of blowing stuff up, they were more happy with graze, although against targets in the forward area the infantry who had to plough through the craters probably had a view as well.
Interestingly RN and I think coast RGA seem to have used base instead of nose fuzes on their AP shells with an explosive fill, although these would have had a graze type action. Don't know (haven't looked) if base fuzes were used with superheavy arty on the W Front. If you wanted deep penetration then they'd probably be better than nose fuzes which were more vulnerable to impact damage causing malfunctions.
Of course using arty to destroy point targets wasn't a very good solution, but there wasn't an alternative in WW1. Probability theory is the god of all true gunners (I abase myself daily), and demands a lot of shells to hit a small target (not forgetting continuous observation to ensure the mpi doesn't drift away from the target as the gun warms, meteor changes, etc).