The Bristol Blenheim's Strafing Potential

[Juha Tompuri]

might also have noticed, they show that it was not the distance that caused the your type claimed penetration drop:

Look again...

These results are supported by tests carried out by the British in January 1941 to compare British and German rifle-calibre steel-cored AP ammunition. The performance of the .303" (11.28 g at 735 m/s) and the 7.92 mm (of unspecified type, but measured at 11.53 g at 788 m/s) was first tested against "homogeneous hard armour". The thickness necessary to achieve immunity from this ammunition at 183 m was 12.0 mm for the .303", 12.5 mm for the 7.92 mm, when striking "at normal" to the armour (i.e. at 90º). The British ammunition was significantly worse when the striking angle changed to 70º; only 6.6 mm was needed for immunity in comparison with 8.9 mm to protect against the German round.

The test then changed to shooting at the rear of the long-suffering Bristol Blenheim at the same distance, involving penetrating the rear fuselage before reaching the 4 mm armour plate protecting the rear gunner, which was angled at 60º to the line of fire. The results in this case were reversed; 33% of the .303" rounds reached the armour and 6% penetrated it. In contrast, only 23% of the 7.92 mm bullets reached the armour, and just 1% penetrated. The British speculated that the degree of stability of the bullets (determined by the bullet design and the gun's rifling) might have accounted for these differences.

There was no distance difference between those two sets of tests. Tony Williams notes they were carried out at the "same distance".

That is not the point.
The starting point of your claim was that the both ammo performance was

the "same" at 100 yards/100 metres?

The point is that you claimed basing on this:

Tests by the RAF indicated that both the .303 and 7.92mm AP bullets had some problems penetrating the structure of the relatively small and light Blenheim bomber. Both guns were fired at a range of 200 yards (180m) through the rear fuselage at the 4 mm armour plate protecting the rear gunner, which was angled at 60º to the line of fire. The results were poor; only 33% of the .303" rounds reached the armour (the rest being deflected or absorbed by the structure) and 6% penetrated it. In contrast, only 23% of the 7.92 mm bullets reached the armour, and just 1% penetrated.

that:

If you remember, I did say last night that "If a given .303 AP round penetrates 10mm of armour at 100 yards "practically" every time...penetration will of course drop off with distance..." The SmK's certainly did...and quite significantly more than the .303 AP's...

Regards, Juha

[phylo_roadking]

The starting point of your claim was that the both ammo performance was

phylo_roadking wrote:
the "same" at 100 yards/100 metres?

No; my starting point was that according to the material brought to the thread as of that point, the performance was the same at c.100 yards. And it wasn't my statement, remember? http://forum.axishistory.com/viewtopic. ... 5#p1926495 It was Knouterer's...

Like other nations, the British had rifle-calibre armour piercing ammo - it wasn't exactly new technology by 1940. And the RAF used it on a large scale.
From a 1929 War Office manual:
"The design therefore takes the form of a hardened steel core enclosed in a bullet envelope, and to enable the bullet to set up in the rifling, a lead sleeve is provided between the core and the envelope. (...) This bullet is used is used in conjunction with an ordinary Mark VII case loaded so as to give a nominal muzzle velocity of 2,500 feet per second.(...) With well made cores this bullet should penetrate a 10 millimetre armour plate of good quality at 100 yards practically every time."

Ammunition destined for the RAF ("Red Label") was subject to more stringent quality control, to minimize the risk of hangfires and misfires.

I might add that with a fighter strafing targets on the ground (or at sea) you have to add the speed of the plane itself to the muzzle velocity, which would make another 300 fps or so and increase penetration somewhat.

There's no reason to believe that the British rounds were markedly less effective than German rounds of very similar construction. That bullets would tend to glance off armour plate angled at 60° is hardly surprising, the same would happen to German bullets.

In fact, a German Army manual gives the same performance for the SmK (Spitzgeschoss mit Kern) round: "Durchschlagsleistung etwa 10 mm auf 100 m".

The point is that you claimed basing on this:

Tests by the RAF indicated that both the .303 and 7.92mm AP bullets had some problems penetrating the structure of the relatively small and light Blenheim bomber. Both guns were fired at a range of 200 yards (180m) through the rear fuselage at the 4 mm armour plate protecting the rear gunner, which was angled at 60º to the line of fire. The results were poor; only 33% of the .303" rounds reached the armour (the rest being deflected or absorbed by the structure) and 6% penetrated it. In contrast, only 23% of the 7.92 mm bullets reached the armour, and just 1% penetrated.

that:

phylo_roadking wrote:
If you remember, I did say last night that "If a given .303 AP round penetrates 10mm of armour at 100 yards "practically" every time...penetration will of course drop off with distance..." The SmK's certainly did...and quite significantly more than the .303 AP's...

And? Penetration DOES drop off over distance...http://forum.axishistory.com/viewtopic.php?t=84321

Most WW2-era rifle-calibre AP had a fairly standard performance, being able to penetrate a maximum of 10-12mm armour plate at short range and at 'normal angle' (a 90 degree hit - the best for penetration). Obviously, this fell off a lot at less favourable angles and/or longer ranges.

...according to Tony Williams.

[Juha Tompuri]

To repeat myself - Which figure does it give in Robert Hurst's material? That's the figure I'm referring to.

AFAIK Robert does not mention anything about turret depression angles.

QED.

Yes, the one already mentioned here:

...Bristol B.-pattern turrets as fitted to the Blenheim, and their angles of depression

I'll repeat myself again; did I say anything about them not being able to clear the tail and control surfaces? No.

You have posted:

phylo_roadking wrote:
...the empennage (let alone the fuselage!) is in the way for strafing below the horizontal.

phylo_roadking wrote:
To be as precise as I can - I did not say that they were unable to clear the tail and control surfaces.

As above.

Indeed. I didn't say they were unable to clear the tail and control surfaces. But the gunner would have to take his finger off the button and stop firing...

And no matter what he's firing at, at what position on sea, or on the ground....if he isn't firing, he's not strafing.

What I said was that the traverse of the Bristol B.-pattern turrets as fitted to the Blenheim, and their angles of depression available to the gunner...vs. placement of the tail and control surfaces....were not conducive to the dorsal turret gunner strafing surface shipping.

Well, you have also claimed

phylo_roadking wrote:
....and 32 degrees' of depression

Isn't it in addition to the normal plane banking, quite good for strafing?
32 degrees is, of course, a bit more than

phylo_roadking wrote:
...not conducive

You still haven't got your think hat on...you're only thinking in one dimension at a time

A more simple question for you: do you claim that the Blenheim dorsal gunner can't use his gun at the your mentioned -32 degree angle?

Regards

[phylo_roadking]

A more simple question for you: do you claim that the Blenheim dorsal gunner can't use his gun at the your mentioned -32 degree angle?

Regards

No. What I've said quite clearly....and several times now....is -

The traverse of the Bristol B.-pattern turrets as fitted to the Blenheim, and their angles of depression available to the gunner...vs. placement of the tail and control surfaces....were not conducive to the dorsal turret gunner strafing surface shipping.

There's a far more simple question you could ask, you know....

[Juha Tompuri]

The starting point of your claim was that the both ammo performance was

phylo_roadking wrote:
the "same" at 100 yards/100 metres?

No; my starting point was that according to the material brought to the thread as of that point

So, no problem, there was material enough availlable for those interested in.

the performance was the same at c.100 yards. And it wasn't my statement, remember?

Perfectly clear. As clear as you used it as one of the basis of your speculation.

And? Penetration DOES drop off over distance

Some less, some more, (some even don't) depending on the ammo type in general.
But seems not the way you have initially claimed.

Most WW2-era rifle-calibre AP had a fairly standard performance, being able to penetrate a maximum of 10-12mm armour plate at short range and at 'normal angle' (a 90 degree hit - the best for penetration). Obviously, this fell off a lot at less favourable angles and/or longer ranges.

...according to Tony Williams.

Yes

But... this claim of yours with it's reasonning does not fit to either of the above;

...If you remember, I did say last night that "If a given .303 AP round penetrates 10mm of armour at 100 yards "practically" every time...penetration will of course drop off with distance..." The SmK's certainly did...and quite significantly more than the .303 AP's...

As you seem not to (have) understand/stood the different factors at the test that affected to the test outcome (penetration figures).

Regards, Juha

[Juha Tompuri]

A more simple question for you: do you claim that the Blenheim dorsal gunner can't use his gun at the your mentioned -32 degree angle?

Regards

No

Another simple question for you.
What is the max depression of Blenheim dorsal gun, the gunner can use?

Regards, Juha

[Juha Tompuri]

A more simple question for you: do you claim that the Blenheim dorsal gunner can't use his gun at the your mentioned -32 degree angle?

Regards

No

Another simple question for you.
What is the max depression of Blenheim dorsal gun, the gunner can use?

After all - that little designed-in "overlap" to the rear that allowed the gun(s) to fire directly behind the tail of the aircraft that you're making so much of...does not assist at all when strafing a ground target. Why? Because while it might allow the gunner to fire at an airborne target attacking directly from the rear...
...the empennage (let alone the fuselage!) is in the way for strafing below the horizontal.

Wouldn't the (apparent) increase of the gun traverse (in addition to the turret traverse) increase the rear gunner field of fire and so also assist strafing a ground target?

Regards, Juha

[phylo_roadking]

No; my starting point was that according to the material brought to the thread as of that point

So, no problem, there was material enough availlable for those interested in.

Not at that point, no. NOW there is, courtesy of the extra information regarding the British tests you brought to the thread. Its those results that change the complexion.

And thus...

..If you remember, I did say last night that "If a given .303 AP round penetrates 10mm of armour at 100 yards "practically" every time...penetration will of course drop off with distance..." The SmK's certainly did...and quite significantly more than the .303 AP's...

As you seem not to (have) understand/stood the different factors at the test that affected to the test outcome (penetration figures).

I did indeed understand the different factors in the test outcome as per the poriginal material of Tony Williams' that I found.

NOW...as I noted above...we know far more about the various different factors influencing the test outcomes. Including a whole different set of tests.

Another simple question for you.
What is the max depression of Blenheim dorsal gun, the gunner can use?

I'm not aware of anything in Robert Hurst's material that says the gunner can't use the full listed 32 degrees of depression. Are you?

Wouldn't the (apparent) increase of the gun traverse (in addition to the turret traverse) increase the rear gunner field of fire and so also assist strafing a ground target?

You seem to be assuming that when I say...

The traverse of the Bristol B.-pattern turrets as fitted to the Blenheim, and their angles of depression available to the gunner...vs. placement of the tail and control surfaces....were not conducive to the dorsal turret gunner strafing surface shipping.

...that the actual field of fire was the sole problem?

It is by no means the only issue. There's another factor in that sentence you have missed.

[Urmel]

I don't see depressing guns in the turret as a limiting factor. The pilot can always tilt the plane as well while circling the target to enable strafing from the turret. There is no law of physics that compels him to keep the wings level.

[Juha Tompuri]

I don't see depressing guns in the turret as a limiting factor. The pilot can always tilt the plane as well while circling the target to enable strafing from the turret. There is no law of physics that compels him to keep the wings level.

Yep.

What I said was that the traverse of the Bristol B.-pattern turrets as fitted to the Blenheim, and their angles of depression available to the gunner...vs. placement of the tail and control surfaces....were not conducive to the dorsal turret gunner strafing surface shipping.

Well, you have also claimed

....and 32 degrees' of depression.

Isn't it in addition to the normal plane banking, quite good for strafing?
32 degrees is, of course, a bit more than

...not conducive

Regards, Juha

[Juha Tompuri]

No; my starting point was that according to the material brought to the thread as of that point

So, no problem, there was material enough availlable for those interested in.

Not at that point, no.

The material was availlable there even before you posted your claim.

But anyway... somehow it seems that you are trying to make things look far more complicated than they in reality are.
You posted here wrong assumption, based on bad/incomplete research and some lack of understanding.
I did a favour to you and corrected it.
Now everything is fine.

Regards, Juha

[Juha Tompuri]

Another simple question for you.
What is the max depression of Blenheim dorsal gun, the gunner can use?

I'm not aware of anything in Robert Hurst's material that says the gunner can't use the full listed 32 degrees of depression. Are you?

No, it was because of your material I asked about it:

that little designed-in "overlap" to the rear that allowed the gun(s) to fire directly behind the tail of the aircraft that you're making so much of...does not assist at all when strafing a ground target. Why? Because while it might allow the gunner to fire at an airborne target attacking directly from the rear...
...the empennage (let alone the fuselage!) is in the way for strafing below the horizontal.

Wouldn't the (apparent) increase of the gun traverse (in addition to the turret traverse) increase the rear gunner field of fire and so also assist strafing a ground target?

You seem to be assuming that when I say...

The traverse of the Bristol B.-pattern turrets as fitted to the Blenheim, and their angles of depression available to the gunner...vs. placement of the tail and control surfaces....were not conducive to the dorsal turret gunner strafing surface shipping.

You assume wrong.

...that the actual field of fire was the sole problem?

Not the sole problem, but the gun traverse claims, independent from the turret traverse, you call:

that little designed-in "overlap" to the rear that allowed the gun(s) to fire directly behind the tail of the aircraft that you're making so much of...does not assist at all when strafing a ground target. Why? Because while it might allow the gunner to fire at an airborne target attacking directly from the rear...
...the empennage (let alone the fuselage!) is in the way for strafing below the horizontal.

.. I must say, I don't understand.

...that the actual field of fire was the sole problem?

It is by no means the only issue.

As not being the sole problem, so not being the only issue.
But when discussing about Blenheim dorsal gun strafing capabilities, I think it possibly is quite important matter to understand.

There's another factor in that sentence you have missed.

Please don't keep on hiding that factor.
If it is possible to you, why not sharing that piece of information?

Regards, Juha

[Juha Tompuri]

About what Jon Lake actually wrote, and how he was quoted here:

And anyway - from October 1940 on, after trials at the RAE the RAF began removing the dorsal turrets from their remaining four squadrons of IFs..Nos. 604, 23, 25, and 219...to improve their performance. (Jon Lake)

from October 1940 on..RAF began removing the dorsal turrets from their remaining four squadrons of IFs ???
Serious?
I think that RAF had more IF equipped squadrons than the four ones you claimed to have been the four remaining ...from October 1940 on.
In reality the four mentioned squadrons seem to have been Fighter Command night fighters/intruders.

And anyway - from October 1940 on, after trials at the RAE the RAF began removing the dorsal turrets from their remaining four squadrons of IFs..Nos. 604, 23, 25, and 219...to improve their performance.

from October 1940 on..RAF began removing the dorsal turrets from their remaining four squadrons of IFs ???
Serious?

Yes.

...On 2 October 1940, Fighter Command ordered that the 64 aircraft equipping its four Blenheim IF squadrons should be thus modified...
...No 604 Sqn began modifying its aircraft that month, with Nos 25, 219 and 23 following suit, albeit slowly...

Regards, Juha

[Juha Tompuri]

That also giving the rear gun some "extra" traverse.

...the gun.

After all - that little designed-in "overlap" to the rear that allowed the gun(s) to fire directly behind the tail of the aircraft that you're making so much of...does not assist at all when strafing a ground target. Why? Because while it might allow the gunner to fire at an airborne target attacking directly from the rear...



...the empennage (let alone the fuselage!) is in the way for strafing below the horizontal.

That little designed-in no-assist: