199 PTTF vs 207 clockwork fuze on 3.7" AA?

[Darkman]

Could someone tell me the criteria or conditions around when a No. 199 powder fuze or a No. 207 mechanical clockwork fuze was used on 3.7" AA shells during WW2? I presume it has something to do with inconsistent burning time of the powder under certain conditions, but I would like to know for sure what the actual reasons are.

Thanks,

Graeme

 

[glevum]

In Hogg's british and american artillery of World War 2 he states that the early 3.7 HE shells were fuzed with 199 or 223 and later ones were fuzed with 207, 208 or 214.

The Shrapnel shell was fuzed with 199 but declared obsolescent in 1943

 

[Darkman]

Can anyone tell me what the criteria for use of each fuze was?
The 199 and 207 fuzes both have graduations up to 30 seconds, so burn time limitations or altitude ceiling is not the reason.

Thanks,

Graeme

 

[Alpini]

I presume it has something to do with inconsistent burning time of the powder under certain conditions

That's absolutely right. Especially in high altitude (lower air pressure) the burning time got more and more inconsistent. That was the main problem when such a fuze was used in anti aircraft firing were most accurate timing was needed.

 

[Bellifortis]

Already in WW 1 powder delay fuzes were near to useless for AA work. I think that I read that 20000 rounds were used in the average to bring down a plane. The very much increased speed of planes in WW2 made them absolutely useless for AA work. Even with mechanical fuzes, ranging equipment and electrical fuze setters it is very difficult and kind of luck to hit a plane at those speeds. They were shooting curtains, similar to the naval small caliber cannon last ditch defence against sea skimming rockets nowadays, hoping that one of the thousands of rounds fired in a very short timeframe, will hit. Only the VT-fuze was an answer to that problem.