AHC: Peerless Air Ministry

[Errolwi]

As to the Political situation with the ANZAC’s ITTL they are of course much better as the losses of OTL in dead headed interventions have not occurred.

And perhaps more importantly the Australian and NZ Governments and theater commanders have not been lied to by the British, destroying trust. They expected pressure to split up forces (Blamey thought Freyberg too trusting early on, and he was right - see a bunch of nicked signalers, and the LRDG sent to the Greek islands), but not Governments and commanders each being told that the other had agreed to stupid military operations for low-probability political benefits.

 

[sonofpegasus]

OTL the ANZACS were IMVHO undoubtable badly abused by the British as their allies. ITL that has not taken place so far and this could create a huge set of butterflies come the winter of 1941.

 

[Errolwi]

Your choice of word to describe the later part of 1941 indicates part of the problem!!!
Looking forward to some RNZAF pilots and ground crew getting somewhat more effective mounts, wherever that may turn out being!

 

[steamboy]

Your choice of word to describe the later part of 1941 indicates part of the problem!!!
Looking forward to some RNZAF pilots and ground crew getting somewhat more effective mounts, wherever that may turn out being!

And the RNZAF pilots looked up and cried out "Martin Bakers!"

And Son of Pegasus looked down and said "Yes."

 

[sonofpegasus]

Actually ITL I was thinking Spitfire Mark V at Darwin (4 x20mm cannon, long range ) with GCI Radar. That is even if the Japanese get that close!

 

[Errolwi]

I imagine some RNZAF pilots in RAF or Article XV squadrons will get MBs, but RNZAF ground crew only operated in the Far East briefly OTL, otherwise with RNZAF squadrons in the Pacific. I can't see the NZ government getting its hands on such sweet gear for relative backwaters.

 

[Errolwi]

Actually ITL I was thinking Spitfire Mark V at Darwin (4 x20mm cannon, long range ) with GCI Radar. That is even if the Japanese get that close!

Hmm. Timor? Maybe not, not Aussie. Rabaul?

 

[sonofpegasus]

12. 43 The war continues elsewhere.

Whilst the Middle East was the epicentre of military operations at this stage of the war for the Army both the Air Force and the Navy were also busy elsewhere.

At sea, the battle of the convoys was becoming more bitter. The advent of Lend Lease meant that even more cargo was available to flow into British ports and every ton was needed and required escorting across the seas. The American decision to actively escort British and American ship almost to the mid point of the Atlantic did much to ease the strain on the RN escort ships. The constant improvement of the Maritime Command aircraft was certainly aiding in the defence of the convoys. However the ability of aircraft to find U-boats was currently far in advance of their ability to destroy them either by day or night. In daylight the main problem was that the U-boat almost invariably saw the aircraft with sufficient time to dive and thence evade the attack. At night even with the aid of ASV RDF equipment the problem was actually seeing the target in a timely manner so that an accurate attack could be carried out. Even when such an attack was actually made hitting the target was more a matter of luck than judgement as at the start of the war there was not a practical low level bomb sight in service.

So in the early part of nineteen forty the Airborne Maritime Warfare Committee (A.M.W.C. known rather jokingly as the Morning Toilet ) had drawn up a list of priorities, which were these in no particular order of importance, as they were all considered interdependent in solving the problems and improving the breed.

Development of a low level Bomb Sight.

Development of a more effective shallow setting depth charge or bomb.

Means of illuminating a surfaced U-boat at night

Guns to attack Submarines as the aircraft approached.

Rockets as above.

Means of detecting a submerged submarine and tracking it.

Better long range/long endurance aircraft.

Long range electronic navigation aids.

Now in June the AMWC report on progress had been presented to the AM and CAS by Tizard.

Despite obstructionism by some RAF officers in Bomber Command generally the scientists were reporting that cross command cooperation especially in technical matters were showing real progress.

One example given was the full introduction of the Mark XIV bombsight into Bomber Command, this had been much helped by the specially trained Maritime Command crews who had been using it in conjunction with RDF to mark coastal targets. With the mass production of the Mk XIV underway Patrick Blackett had been able to transfer his attentions to solving the low level bomb sight problem that had been vexing both the Admiralty and Maritime Command. Using the XIV as a starting point Patrick Blackett and his team had in a remarkably short time produced the first working models of what would become the Low level bomb sight mark III and slightly later the Mark XV bomb sight. One advantage of the Mark XIV bomb sight was that the sight its self fitted the same mounting as its forerunner the Course Correct Bombe Sight, this was made possible by having the ‘Bombing computer’ built as a separate unit mounted on the aircraft fuselage. The initial versions of the Mark WIV as used in the early raids led by Maritime Command aircraft had required continual manual inputs to update the computer but the production version now had automatic updating directly from the aircrafts instruments once the initial parameters had been set.

So to make the new low level mark III bomb sight a new ‘Bombing Computer’ unit designed to solve the angular velocity of the aircraft relative to the target was developed. Unlike the Mark XIV the Mark III low level sight did not require wind speed calculations or course settings the only inputs needed were the aircraft altitude and speed. The Mark III had manual input for altitude and continuous automatic airspeed input. The sight head itself was based on the mark XIV with a reflector surface on with a horizontal line of light was projected travelling down the sight at the calculated angular velocity required to hit the target, when the target and line travelled at the same speed down the glass screen they would become super imposed at which point the bomb aimer dropped the weapons.

By Easter 1941 bombing errors of less than twenty yards were being recorded on targets moving at up to eight knots with a drop height of one thousand feet. From eight hundred feet that error was more than halved and from four hundred feet was reduced to a quarter. Whilst the Mark III was a great improvement Blackett was concerned about the potential errors caused by the need to pre-set the altitude for the attack. To correct this Blackett and his team were working on what would become the Mark XV sight that used the input from a radio altimeter to provide continuous automatic altitude corrections. Whilst this sight had been developed principally for attacking surface U-Boats it was quickly apparent to Maritime Command that the kind of accuracy being achieved made it possible to attack and sink small vessels and those in shallow water by using bombs rather than torpedoes. This would have some major benefits, one being that torpedoes were expensive. Secondly that a bomber could not only attack from a higher altitude but could approach at a speed many times faster than the current torpedoes could be launched at.

Another advantage that the Mark XV would have was that with suitable modification it could be mounted in the cockpit and used by the pilot in an aircraft that did not have a bomb aimer’s position in the nose of the aircraft. So whilst the radio altimeter and the computer for the Mark XV sight was being developed and tested the Mark III low level sight was put into mass production. The shallow setting fuse and the new airdrop depth charge had been in service for some months but OR and testing had shown that with the accuracy obtainable by the new low level sights a single large depth bomb would be more effective.

The scientists had calculated an optimum size and come up with a new piece of ordinance that had a weight of six hundred pounds, this had resulted in the development of the 600Lb Anti Submarine Bomb Mark I which used a type No 862 tail fuse to detonate the filling of four hundred and thirty nine pounds of Torpex explosive. This would be introduced into service in the second half of nineteen forty one. Trials were ongoing as to the effectiveness of this weapon to stove-in the hull plating of small merchant vessels when they were near missed by the bomb. With the accuracy of the Mark III and the Mark XV it was possible that a near miss could with the correct weapon and depth setting become a kill or at least require dockyard time for the target.

By late nineteen forty the problem of illuminating a surface vessel at night in order to attack it having located it by the use of ASV RDF was self evident not least from Maritime Command aircrew reports.

The situation had been noted by Wing Commander Humphrey de Verd Leigh, an ex RNAS pilot who had re-joined the RAF for the wars duration. This enterprising officer who had spent the interwar years as an engineer in various industries had set out on his own volition to come up with a workable means of illuminating a potential target on the surface of the sea. Once Leigh had with his own resources come up with a design and a proof of concept ground base prototype, Leigh had contacted the AMWC, who had appraised the device and the progress made by Leigh. Immediate steps had been taken by the AMWC to give Leigh the resources to develop and fit a prototype into an aircraft for trials. The aircraft chosen was a mine clearance Wellington, as not only did it have a suitably powerful generator already fitted in the fuselage but the aircraft also had the aperture and mounting ring for a ventral gun turret which could be used to mount the searchlight under the aircraft.

By mid January nineteen forty one Leigh and his team were able to demonstrate a viable twenty four inch diameter searchlight producing a beam with a brightness of some fifty million candelas that could successfully illuminate a surfaced U-boat at the required range. This ‘Leigh Light’ that could be fitted to any aircraft that had a ventral turret position was ordered into priority production. Leigh and his team were aware that this first design was very limited in the aircraft types to which it could be fitted and work was commenced on designing another version of the ‘Leigh Light’ that could be mounted under the wing of virtually any aircraft. This would be utilising a smaller search light of some twenty inches diameter producing some ninety million candelas mounted within a nacelle. The target was to have this version in service by the winter of nineteen forty one.

Aircrews had been requesting forward firing guns to attack U-boats since the commencement of hostilities. The standard forward armament of RAF aircraft at the time consisting of rifle calibre machine guns had proved incapable of doing any significant damage to a submarine. The twenty millimetre cannon as used in the Beaufighter had proved more effective when using armoured piercing ammunition but even this was considered in adequate to do mortal damage to a U-boat. Trials were ongoing with the Vickers S gun, the Rolls Royce BH cannon and the Bofors gun all in forty millimetre calibre. The Vickers S gun and the RR BH both fired the same round as the two pounder Pom Pom gun used by the Navy, thus these guns had considerably lower velocity than the much more powerful Bofors gun. Whilst this lower velocity resulted in less armour penetration it did benefit from much reduced recoil making the guns lighter and easier to mount in an aircraft.

Some Maritime Command aircraft were already mounting forward firing twenty millimetre cannons and a experimental aircraft was trialling the Vickers S Gun. Meanwhile the RN were carrying out further tests on the capabilities of the various guns and rockets proposed as to their effectiveness in penetrating the hull of a submarine both above and below the water line.



Using sixty eight pound rockets for anti shipping attacks was already being in combat by the RAF and Maritime Command who were now investigating the practicality of carrying rockets on long range patrol aircraft. One problem encountered so far was finding a suitable place to carry and fire the rockets from on the variety of aircraft being used by Maritime Command. This work was on going and was more problematical the bigger the aircraft was. In simple terms the small wingspan of fighter aircraft meant that the rockets were close enough to the point of aim that the point of convergence of the missiles was not too range sensitive. The greater the wings span the smaller the zone becomes where the rockets flight path intersect to give a reasonable expectation of hitting the intended target.

The solution would be to mount the missiles on the fuselage or very close to it and this was not easy. So far the best solution found was a pair of stub wings forward of the inboard engines and clear of the propellers.

A joint team from the RAF and the RN were working on various technologies in an effort to produce a practical method of both locating and tracking a submerged submarine. Current reports seemed to indicate that any practical equipment was still several years from deployment.

The current long range patrol aircraft were considered adequate and with sufficient development potential to cover any foreseeable requirements at the current time.

Long Range Navigation aids were not the sole remit of Maritime Command and development work on a number of systems and technologies was ongoing with other commands and services. Watson Watt and B.V. Jones had prepared a separate report on the Electronic navigation work directly for the AM. and that was also presented to the AMWC committee for their comments

 

[AlanJWhite]

he twenty millimetre cannon as used in the Beaufighter had proved more effective when using armoured piercing ammunition but even this was considered in adequate to do mortal damage to a U-boat. Trials were ongoing with the Vickers S gun, the Rolls Royce BH cannon and the Bofors gun all in forty millimetre calibre. The Vickers S gun and the RR BH both fired the same round as the two pounder Pom Pom gun used by the Navy, thus these guns had considerably lower velocity than the much more powerful Bofors gun. Whilst this lower velocity resulted in less armour penetration it did benefit from much reduced recoil making the guns lighter and easier to mount in an aircraft.

Ironically before WW2 iOTL the RAF had originally specified a gun that squared that particular circle as the forward armament of the Sunderland
but rather stupidly changed it to rifle calibre machine guns

COW 37 mm gun - Wikipedia

en.wikipedia.org

Though firing a lighter shell than the S gun etc, it did it at a better MV and a higher RoF

 

[sonofpegasus]

As the Vickers S gun was developed from the COW 37mm gun after the Vickers Corporation had bought the Coventry Ordinance Works I had left the COW Gun out as being irrelevant ITTL. However you are quite correct that OTL the RAF had since WW1 been looking at large calibre cannons as anti U-boat armament for its larger flying boats.

 

[AlanJWhite]

As the Vickers S gun was developed from the COW 37mm gun after the Vickers Corporation had bought the Coventry Ordinance Works I had left the COW Gun out as being irrelevant ITTL. However you are quite correct that OTL the RAF had since WW1 been looking at large calibre cannons as anti U-boat armament for its larger flying boats.

Thanks for reminding me that the Cow 37mm was an ancestor of the Vickers 40mm S Gun and also worked on earlier than I remembered.
iOTL it was tested as a defensive gun in a turret on Wellington II well before any need for an antitank weapon for a fighter bomber was identified.

However, the key point iOTL (and rather surprisingly iTTL given the PAM) is that the need for heavy weapons to attack a Uboat on the surface was lost.

The main aim has to be suppressing any defensive fire and hampering the crash-dive
because even a Bofor 40mm is unlikely to pierce the pressure hull though damage to planes, rudders scopes etc is possible.
A penetrating shot needs at least a 57mm like the Tsetse or the American 75mm

The scientists had calculated an optimum size and come up with a new piece of ordinance that had a weight of six hundred pounds,

Given that iTTL the PAM has already developed cluster munitions (and assuming the RN has pushed forward on the scatterable Hedgehog bomb)
I am somewhat surprised that a union of these ideas has not been proposed
and thankfully adopted as the preferred ASW attack for a recently submerged UB - requiring less accuracy and giving confirmation of a kill
(though very limited possibility of cumulative damage)

 

[sonofpegasus]

I must admit that it not crossed my mind that combining an adaption of the Hedgehog anti submarine mine with a cluster bond my provide a viable weapon.
I would welcome people thoughts on that one. could the pattern be reliable enough to ensure a hit. How many Hedgehog mines needed to hit to kill a U-Boat?
Using the Mark III site and the six hundred pound anti submarine mine has a fairly high kill probability and allows the bomber to come in relatively high and fast. How low would the bomber need to be to score a hit with the Hedge hog cluster bomb?
Also how effective would the Hedgehog mines be on a surface or just dive U-Boat? OTL the Hedgehog was designed to kill dived U-Boats.

 

[alspug]

I am not sure a hedge hog projectile is armed before hitting the water. I think from recollection it was a propeller that turned and brought the firing mechanism to a hair trigger, then if it hit anything hard it exploded. The beauty of it as with the Soviet modern RBU systems is it can't be jammed and if you hear it and your within the pattern being alive after is good luck.

As for how many to destroy a Submarine, that a question of depth and location of hit. It is conceivable for a bomb to hit the casing and or conning tower and not kill the Submarine but being operational after is a big no. Warhead is 30 kg according to data so would be fairly effective. The deeper the Sub is the more damage the charge will do.

Soviet RBU is a bigger weapon and a rocket as opposed to a Spigot mortar, The Spigot Mortar works the opposite way to a normal mortar and the PIAT is a great example.

 

[Paulo the Limey]

I must admit that it not crossed my mind that combining an adaption of the Hedgehog anti submarine mine with a cluster bond my provide a viable weapon.
I would welcome people thoughts on that one. could the pattern be reliable enough to ensure a hit. How many Hedgehog mines needed to hit to kill a U-Boat?
Using the Mark III site and the six hundred pound anti submarine mine has a fairly high kill probability and allows the bomber to come in relatively high and fast. How low would the bomber need to be to score a hit with the Hedge hog cluster bomb?
Also how effective would the Hedgehog mines be on a surface or just dive U-Boat? OTL the Hedgehog was designed to kill dived U-Boats.

IIRC hedgehogs were contact fused, so were effective on boats that had just dived. Not sure about surface though, as the fuse might think it had just hit the waters surface, rather than a target. Someone more knowledgeable will hopefully enlighten me, as to how the contact fuse was designed to withstand the initial force of hitting the water yet still trigger when hitting a uboat.

edit-ninja’d by the answer! Cheers @alspug

 

[PMN1]

Might the list also include 'homing' mines....

 

[sonofpegasus]

Fido was an American project started late in 1941, So at the moment does not feature ITTL. Due to the sheer volume of research undertaken in the PAM as it is IMHO adding a British Fido would be beyond the threshold of plausibility and would make this a complete Britwank!

 

[AlanJWhite]

Using the Mark III site and the six hundred pound anti submarine mine has a fairly high kill probability

I would really like to see your source for this conclusion.

If a direct hit could be achieved it should work but the UB is a very small target for a single dropped unguided weapon
(whatever bombsight is used from whatever height )

Worse a near-miss is not good enough
AIUI the size, shape and construction of a UB all make it VERY resistant to any air blast when on the surface no matter how close

If the 600lber is designed to attack a recently submerged UB, e.g. with a delayed fuze so it explodes underwater
it is also unlikely to work without a direct hit contacting the UB hull

A single large explosion in the water is greatly damped by any the water between it and the target
(as Barnes Wallace found with his dam experiments)
The effect is reduced further because the UB hull will move away in response to a blast (unlike a dam wall)
That is why depth charges were always dropped in groups of three or more to bracket the hull between converging pressure waves.

As Alfred Price points out in his classic "Aircraft vs Submarine" weapons that explode on impact with the UB hull are much better at breaching it
which is why the 35lb Torpex warhead on a Hedgehog bomb in contact was enough to kill if it hit in most cases 👍
while a 250lb depth-charge warhead mere yards away would not 👎

OTL the Hedgehog was designed to kill dived U-Boats.

True, but then I was not proposing it to attack a surfaced UB ... for that, a set of "rocket spears" is much better
(and in any case, a fully surfaced target was rare even at night with radar and a Leigh Light.
The target most often had time to attempt a crash dive ...hence the OTL need for shallow set depth charges as standard).

In truth (1) the surfaced UB. (2) the recently dived vessel and (3) a deep below submarine were very different targets
requiring separate attack methods. Therefore iOTL by 1944, some RAF VLR Liberators were carrying

• 6+ rocket spears to deal with UB caught on the surface (plus machine guns to suppress flak and harrass the crew)
• 4 -8 depth charges with true 25ft fuses for a UB that had just submerged
• a pair of FIDO passive acoustic homing torpedoes for a deeper diving target

(that info also from A vs S. I cant give you a page no. I read a lending library copy when I was an impoverished engineer )

You have confirmed that FIDO will not arrive any earlier than OTL
so increasing the effectiveness against a submerged target will be vital

I was suggesting that iTTL the depth charges could be replaced with cluster bombs deploying modified Hedgehog warheads.
Since the bomblets would not require a launching charge they would weigh only ~ 50lbs
allowing 6 or more in a carrier replacing a depth single charge of 450lbs

Therefore a VLR could make 2 separate attacks each equivalent to a shipboard launcher of 24 bombs
Given that a Hedgehog attack proved many times more effective than dropping of a group Depth Charges that would be a significant gain 💥
(even ignoring that a Hedgehog explosion would locate the target for an immediate second attack increasing the chance of a full kill)

With the PAM in place, this could be available by late 1941 at the worst.

BTW You may ask - can a Hedgehog charge work when airdropped?

Naval History Magazine

Bringing the history of the Navy, Marine Corps, and Coast Guard to life.

www.navalhistory.org

This was another airdropped weapon developed by the USN in WW2 that used the Hedgehog warhead
(though through adaptation via the rocket-powered Mousetrap shipboard launcher
and then further modified for use from an aircraft.

Of course, a key factor for the retrobomb was its use alongside an early MAD detector that fixed the location of the target closely
so that it could be deployed in smaller salvos than my proposed cluster carrier method)

 

[sonofpegasus]

Thank you for the appraisal, very interesting article as well.
My statement was made on an assumption (rightly or wrongly) that a 410lb charge of Torpex exploding with an error of 15ft at a depth of 25ft would have a fairly high chance of mission killing a U-boat. Even if the hull is not breached that should cause a shed load of shock damage.
I rather like the idea of your cluster bomb based on the Hedgehog warhead.
This could give the basis for an interesting test in the PAM.
As this retro rocket was an American weapon I would rather leave it as OTL, Once the USA. enters the war in December 1941 then the PAM might get involved.
Do you have a date for the first deployment of spear rockets OTL? I have yet to find a definitive date.

 

[Reggieperrin]

Thank you for the appraisal, very interesting article as well.
My statement was made on an assumption (rightly or wrongly) that a 410lb charge of Torpex exploding with an error of 15ft at a depth of 25ft would have a fairly high chance of mission killing a U-boat. Even if the hull is not breached that should cause a shed load of shock damage.

My understanding is that this is exactly what the OR boffins worked out and from summer 42 onwards a 25 foot setting was used.

15ft is coincidentally about the draft of a Type VII uboat, only a bit less than a light cruiser. So there is plenty of hull to attack even when ‘surfaced’.

 

[AlanJWhite]

My understanding is that this is exactly what the OR boffins worked out and from summer 42 onwards a 25 foot setting was used.

15ft is coincidentally about the draft of a Type VII uboat, only a bit less than a light cruiser. So there is plenty of hull to attack even when ‘surfaced’.

Quite correct that the 25ft setting was calculated by the new team which we now know as "Operational Research"
but that depth was decided as a compromise when the only weapons available were depth charges.

The Charges had previously been set deeper to match the depth that a UB could reach given the average warning time of an incoming plane they had.
(This time was tested in some practical experiments - and did have some benefits in improving RAF plane camouflage)

That use of the "average" was on the (incorrect) assumption that this would give the best results overall
by giving too much importance to at least damaging the maximum number of targets rather than maximising kills and serious hurt to others.

It was only when RAF crews reported that many of the UBs they surprised and straddled had in fact survived the blast from these deeper explosions
the scientists realised that they were missing the opportunity to kill more UBs rather than simply damage to some.
This resulted in the depth setting be set as low as possible (50ft?) and a request being made for a new 25 foot hydrostatic pistol.

Effectively a 25ft depth setting would gather in the low hanging fruit of any UB still in the early stages of its dive
while still offering the (admittedly reduced) possibility of damaging a UB that had been given more warning
and thus moved further horizontally and vertically in an unpredictable direction.

IIRC (and I very well may not since it is 40 years since I read Aircraft vs Submarine)
once the British had rockets that could attack a UB on or near the surface, that combination allowed them to set the charges somewhat deeper again,
Larger MPAR carried both rockets and charges, and could also use any machine guns.
Smaller carrier planes often operated in pairs - one rocket, one charge, sometimes with a fighter for flak suppression.

However, once the USN made the FIDO available i.e. a passive acoustic Homing torpedo that could deal with deeply dived UBs ,
most Depth Charges were again set to 25ft for the recently submerged target.

That "Triple Whammy" was covered in one vivid anecdote of A vs S, whereby an RAF crew expended all 3 systems on one luckless UB.
(admittedly this was an "experten" crew)