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Thread: The N Atlantic Air-Gap - and its reasons

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    Default The N Atlantic Air-Gap - and its reasons

    Dear All,
    I am struggling to understand the problems of the WW2 N Atlantic Air-Gap. OK, many of them were ‘political’ (i.e. Harris had more ‘clout’ than AOC-in-C CC). But a/c had been crossing the Atlantic (in both directions) for many years. Again, OK, they did not have to ‘loiter’ over a convoy doing all of 7 kts in a full F 9 gale. But before I invoke logic and reasoned argument wrt a/c performance figures and distances, does anybody know if any serious thought was given to using the Maia/Mercury concept (for ASW work) which had only been proved a few years before WW2? Was it just TFD, or were there somebody else’s ‘hidden agendas’ at work? After all, a Maia/Mercury combination went direct from UK to S Africa. Plenty, I would have thought, of loiter time over The Pond?!!
    Would appreciate thoughts.
    TIA
    Peter Davies
    Last edited by Resmoroh; 26th May 2013 at 12:04. Reason: Ross, pse correct Oggin spelling! Ta!
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    Hi Peter,

    If you click "Go Advanced" button when in basic edit then thread titles can be edited.

    Ok...quick and dirty version.

    RN pre war had said but out RAF all trade on high seas to be protected by RN vessels.

    Coastal told trade shipping round coast to be Fighter Command tasking.

    So maritime role to be funded was recce for the fleet when not being done by FAA.

    Ergo no large numbers of long range aircraft funded/designed. Sunderland was design for empire trooping and support rather than recce.

    Sunderland production had made the ordered numbers in 1940 and jigs being dismantled at Shorts to allow Stirling Production so restart not high on cards.

    Harris as part of BPC had obtained Hudson and trial Cat at great political uproar and had virtually ignored LR bombers.

    Push for rearming was for Bomber Force then Fighter Force with Coastal making do with stop gaps until Lerwick and Botha appeared in service.

    When Coastal ended up catching all the dropped tasking it had meagre equipment and bases to range far. Invasion of Iceland gave land base but CC still did not have LR equipment in numbers.

    More Cats were ordered to bridge the gap caused by cancellation of Lerwick until Sunderland production could restart in earnest.

    Coastal supplies of ASV were diverted to Fighter Command for night fighters for Blitz giving equipment shortage for closing the gap and Liberator LR aircraft bought for purpose "sticky fingered" by Bomber Command who now saw need to immediate LR heavy bomber.

    Lots more turns and twists but this basically is the tale. Not CC job-when CC task then equipment diverted elsewhere- when equipment available then aircraft attempted to be diverted elsewhere.

    Ross
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    Ross, tks yrs (much appreciated),
    So the reasons are beginning to look ‘political’ rather than ‘technical’? You mention the Stirling. I’ve read (somewhere) that the Stirling – once it was found to be not a good Bomber – would have been better at maritime recce than most?
    My perplexity was based on the following (all figs within +/- 5%):-
    Iceland > Canada 1500 nm
    Iceland > Azores 1565 nm
    N Ireland > Canada 1786 nm
    Bermuda > Azores 1800 nm
    Canada > Azores 1160 nm
    N Ireland > Azores 1230 nm
    (all within the capabilities of a Sunderland (before the LR Liberator became more freely available) - but little 'loiter time').
    Cruising speed of a Sunderland 155 kts
    Range given as 1780 nm, but 14-hr patrols at cruising speed = 2170 nm (don't compute).
    It would seem, therefore, that Harris was quite content for the populace of the UK to starve – quite forgetting that the same problem would have starved his Bomber fleet of much of its fuel (and much of its bomb load)?
    I appreciate that I am a committed (and convicted!) Conspiracy Theorist, but it does seem that not all the CC eqpt decisions, at that time, were properly made?
    Miaia/Mercury combo as an ASW weapon - anybody got any thoughts?
    TIA
    Peter Davies
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    Oh where to start!

    All the sub warfare lessons of 1914-18 had to be re discovered.

    At end of 1918 it was not enough to scarecrow to keep uboat submerged but also needed A/S bomb capability to hit them if they continue to run on the surface. 500Lb bomb was found to minimum optimal and stick of 4 to 6 best compromise.

    During peace years the RN fought to have naval/maritime aircraft returned and as part of this anti RAF lobby (shades of Sharky today) the admiralty convinced the treasury that A/S was all their territory.

    RAF stocks of weapons became 250Lbs instead of the needed 500lbs and bomb sights were designed/procured/trained with for Bomber Command needs.

    Task of bombing capital ships at sea was given to Bomber Command. Task of protecting coastal shipping was given to Fighter Command.

    Treasury only permitted Coastal to retain equipment for A/S declared role and that was Patrolling North Sea between Dover and Shetland-Norway for U and E boats on surface. Once sighted they were supposed to eyeball lob (no calibrated bomb sight) the 4 off 250lbs that the Anson carried and leg it to the closest RN vessel then lead Dark Blue to deal with it in the ways of the Senior Service.

    The land war would be limited to Belgium/France/Holland as before, Bomber Command would be conserved until ready and RN would keep the Kreigsmarine to the Dogger Bank/Jutland or North Sea at the very least.

    With this thought the Western Approaches would need little coverage by any RAF assets only RN at Falmouth/Plymouth etc. This led to the lack of Fighter Command Group/units and Radar to protect coastal trade in this area.

    The main recce aircraft for Coastal was the Anson. Adequate in range for the invisaged tasking to 1938. No money or effort was available to look at development so none was expended until 1939 when the annual exercises showed some of the short comings. GR/TB land Plane spec was released and Botha ordered off the drawing board but until it appeared Hudson was to be provided. Still no requirement for 500lb ers or ASV.

    London flying boats were providing the longer range recce for the greater distances beyond Shetland to Faroes but only Dawn and Dusk flight needed per day so 6 or so aircraft at max needed. Communication with Gib, Alexandria, Steamer Point etc to Singapore was with Sunderland so again not too many aircraft needed hence the low number ordered. No need to build any more as LR Flying Boat spec had been issued and twin engine Lerwick was ordered off the board.

    So 1st Sept 1939 treasury had it all covered. Stop gaps in place, eventual equipment designed and on order, tasking split up and Commands equipped with needed gear for the task.

    2nd Sept 1939 - all gone to hell in a hand cart for the A/S tasking of Coastal. Most of the U-boats into the Atlantic during the time Coastal was on war footing exercise looking for exactly that. Closely followed by a few of the capital ships. All down to RN in Atlantic now.

    5th Sept 1939 - Full bombload from Anson, perfectly dropped fails to damage submarine - back to trials - found needs 500lb bombs in stick 6 to 8 dropped and with capability to explode at depth. None in arsenal need to be developed and supplied.

    4-5-6-7 Sept Bomber Command fails dismally in not only finding reported marine units at sea and bombing them but also in being able to bomb them when stationary at anchor in Roads.

    Coastal resources moved to plug the Bomber Command tasking. Ansons n.b.g. for Bombing and now A/S role so only Sunderland/London/Hudson can be deployed. Cupboard bare for any Atlantic work but also no means of "seeing" target apart from Mk1 eyeball. Convoy system being set up as knee jerk so no RN escort to call up.

    Fast Forward to April 1940 no real change all effort and money being expended to raise Fighter Command to minimum equipment levels.

    U-boats of time are short ranged so most have returned to Germany after first en-mass war patrol and now acting independently off Ireland/Southern Approaches. Some ASV gear for Hudson and Sunderland and first depth charges appearing. So the gear and aircraft are starting to appear in place.

    Norway is game changer - Sunderland is only aircraft with range to support allied operations in far North so aircraft diverted to moving bods for Army and recce for RN units. In the south the Hudsons needed for recce of German landings. Move all the pawns for this.

    May/June 1940 Sunderlands (and your Empire G and C class flying boats with broomsticks as machine guns) still occupied in North but Hudson/Ansons are needed for coastal operations off the low countries so all pawns move again.

    July/Aug/Sept 1940 North sea now hostile territory from Norway to France. All tasking as per May/June 1940 but with addition of east coast trade protection tasking dropped by Fighter Command because Dowding System not effective in allowing them to operate forward of CH radar (over 5 miles or so of coast). Ansons and Hudson now anti-shipping, anti-e boat and anti invasion barges.

    Italy has advanced into the western desert and Sudan/East Africa, France no longer capable of keeping western entry to med safe so Sunderlands and Empire flying boats diverted to Med/Alexandria for med fleet recce duties. Bomber and Coastal Recce units from Far East moved to canal zone.

    In 1941 most of these demands on the long range Sunderlands are still in being but ASV and bombs to be fitted to any capable aircraft are not, neither are crews available as manpower has gone to Fighter and Bomber Command to replace losses. So magic wand of more Sunderlands or one extra composite would not appease the general situation.

    Failure of Botha and Lerwick in service so advantage of new type numbers wiped off ORBAT.

    Cats and Liberators coming in to release Hampden and Whitley for other tasking. Blenheim transferred from Fighter Command and Bomber command to make up needs of east coast trade protection and long range fighter trade protection for Southern Approaches.

    U-boats now based on the Atlantic with longer ranged types so can range further into Atlantic and pack tactics in place.

    Sunderlands tied up recce for fleet in Shetland and Med, move of uboats down African coast so Sunderlands deployed round north Africa in addition to original areas.

    USN reporting U-boats in plain r/t so "gap" really stretches to US coast. No real numbers of Empire Boats and Clippers to fill this area effectively.

    Dec 1941 again all change. Trooping and supply routes to India and Far East increased. East coast of Africa and East Coast of India need maritime support, Cats and Sunderands creamed off Home waters/West Africa and diverted. U-boats act off US seaboard. US a/s capability limited so 2 squadrons of UK Hudsons sent to Florida/Gulf to bolster response.

    It's only at this point that the "gap" was created, up until now the U-boats were mainly attacking shipping in concentration areas which were mostly within land based aircraft range. The kill rate of the Coastal forces had not forced the U-Boats into the middle of the Atlantic in any great numbers. So up to this point there was no pressing need for more or alternative long range sub killers.

    Your answer of Empire boats was to a problem that did not really exist until Mid 1942.

    The combination role was for the parent flying boat to give the final range and carry the most payload while the small seaplane was to be detached close to it's intermediate destination with a light mail package. The packet seaplane had no real range so needed somewhere to go when detached which was too small to allow economic landing/takeoff of the larger flying boat. Where would your ASV combination go when detached?

    You are quick to place the problems of the "gap" at Harris but in reality he is a bit player until becoming AOCinC Bomber Command in 1943 a few years after the seeds were sown for the creation of the gap.

    Enough to digest for now.

    Regards
    Ross
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    Ross has given an excellent overview of the politcal/strategical issues. There are some technical and tactical issues to consider as well. The technical issues were discussed last year over at the TOCH forum, I will try to summarize them.

    Peter, a typical airplane has two "best" cruising speeds. Best endurance is generally at a very low speed (techies call it minimum power speed), and results in short range. Best range will occur at a higher speed, and probably a higher altitude - neither being suitable for ASW work 1930s style. (Think of best range speed as best miles per gallon.) The difference between these 2 speeds can be quite large, particularly with 1930s style thick wings. As a result, it is not easy to look at published range numbers and draw accurate conclusions about "useful" ranges in a different role. As a rough rule of thumb, you can assume 25% to 33% of a maximum range number would be a good first guess for a useful patrol radius. Thus your 1780 nm range of a Sunderland means roughly 460 to 600 miles radius. This assumes same fuel load and cruise conditions as used for the maximum range - as Ross pointed out, the need for a goodly number of 500 pound bombs could reduce the fuel load and that reduces the useful radius even further.

    Ross briefly mentioned the tactics used for ASW and how they evolved over the war, I can expand on this a bit from the RCAF point of view. Conventional wisdom in 1939 was that the ASW aircraft would stick close to the convoy, preferably in continuous visual contact. Also, low altitude was prefered to improve accuracy of observation, and to increase the chance of attacking a spotted sub before it had time to dive (it was assumed the sub saw the aircraft at the same time the aircraft saw it.) . This means your aircraft is operating at minimum power speeds and low altitudes, thus the range drops from the "best case" numbers manufacturers love to use, and the 25% to 33% calculation now gives you a useful mission radius of something less than 460 nm for a Sunderland. Possibly much less. Thus, when the need for mid ocean patrols developed, you had an air gap.

    The RCAF and the RAF both did regular ongoing statical analysis of their aircraft patrols, and worked on developing new tactics right up to the end of the war (and beyond). Two general trends emerged that gradually helped close the air gap. First - aircraft began operating at higher and higher altitudes. This allowed them to cover more square miles of ocean per flight hour, and operate at better miles per gallon. New colour schemes, new attack techniques and new weapons allowed the aircraft to still catch the sub before it submerged. That is a quick summary of a topic that diserves a book or two.

    Secondly, aircraft began to operate independantly of the convoys, in areas where the subs were expected to be. This was aided by ongoing improvements in signals itelligence that helped the RCAF/RAF figure out where subs were likely to be at any given time. Today we call these "barrier patrols", as opposed to convoy escort patrols. Free of pacing convoys, cruise speeds could increase, towards best mileage speed.

    For the RCAF, the effects of all these became very apparent in the summer of 1943. Two Liberators of 10 (BR) Squadron were ferried between various stations to provide coverage for Winston Churchill's visit to Canada, and these 2 aircraft made more sub sightings and attacks during their transit flights than the rest of Eastern Air Command combined during the same time period. All at "best range" altitudes and speeds, free of convoys.

    These changes in tactics did as much to close the air gap as the introduction of longer range aircraft. I have to agree with Ross that you can't really blame Harris for any of this. He was just doing what every other senior RAF and RCAF officer did at the time: apply the knowledge they had, and the equipment they had, to the problem as they understood it. It is very easy after the fact to say the knowledge was wrong, the equipment was inadequate, and their understanding of the problem was not complete. That's life.

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    Cheers Bill,

    Some time ago I came across a file that contained a pile of "operational use its" facts for Coastal. It also contained actual war loads to be used rather than theoretical. Some of the types cleared are surprising.

    (450 lb was the light case replacement for the early war 500lb DC)

    AIR15/549 gives the standard patrol depth charge loads for Coastal Command.

    The list of aircraft makes interesting reading.

    For 450lb depth charges:
    Blenheim 2
    Beaufort 4
    Vildebeest 2
    London 2
    Lerwick 4
    Sunderland 4
    Whitley 4
    Catalina 4
    Hampden 4
    Wellington 6
    Stirling 24
    Manchester 15
    Halifax 15
    Hudson -
    Albemarle 6

    250lb DC
    Blenheim 4
    Beaufort 6
    Vildebeest 4
    London 4
    Lerwick 8
    Sunderland 8
    Whitley 10 or 12
    Catalina 8
    Hampden 4
    Wellington 6
    Stirling 24
    Manchester 15
    Halifax 15
    Hudson 4
    Albemarle 9

    Regards
    Ross
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    Very interesting Ross. For the RCAF in September 1939 the aircraft used for ASW patrols included the Atlas, Wapitis and Lysanders. Like the RAF, they assumed ASW meant coastal and harbour patrols. Mid ocean was left to the Navy.

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    The DC load chart was for mid war but also in AIR 15 is the following list for early war:

    Type, Economical True speed at 2000 ft, 80% range and endurance in still air, Bomb load with nominal tankage
    Anson, 114 kts/25 galls per hr, 510 sea miles/4:50 hrs, 2 x 100 lb
    Hudson, 165 kts/71 galls per hr, 990 sea miles/6 hrs, 4 x 250 lb
    London, 86 kts/120 galls per hr, 450 sea miles/5:20 hrs, (8 sic) x 250 lb
    Stranraer, 92 kts/55 galls per hr, 660 sea miles/7:20 hrs, 4 x 250 lb
    Sunderland, 137 kts/130 galls per hr, 1,700 sea miles/12:40 hrs, 8 x 250 lb

    Regards
    Ross
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    Just to pick up on a few technical points initially - max range speed is faster than max endurance speed with jet engines, but they should be the same with piston engines. However, maximum range distance is always quoted without payload into zero wind, let alone considering realistic operating allowances (reserves) or any patrol time. As a rule of thumb, a realistic tactical radius is about a quarter of the quoted range and only very rarely better than a third. Variations are legion, of course.

    Harris was only fighting his corner, looking after that aspect of the war for which he had been given responsibility. That's what every commander has to do, and is supposed to do. Any blame for permitting excessive hoarding of long-range assets has to be placed higher, which means Portal and Churchill. Everybody and his aunt wanted long-range aircraft, on every front. It was decided at high level that a bomber campaign against Germany stood the best chance of leading to eventual victory. That couldn't be achieved without the building up of large forces.

    It is worth adding here that from December 1941 the US was also in the war - it could have redirected some of its heavy bombers to the Atlantic but had exactly the same level of demand on their use. Of course, to question this isn't as fashionable as it is to slag off Harris.

    There's another defence for a convoy that was even rarer than LRP aircraft - trade protection carriers.

    In the end, it should be remembered that Bomber Command destroyed more U-boats than Coastal Command did.

    PS The Botha was designed to the same specification as the more successful Beaufort, as an anti-shipping strike aircraft not as any kind of patrol aircraft. It was pressed briefly into use on patrol duties because it was accepted as being no use for any other combat role.
    Last edited by Graham Boak; 26th May 2013 at 21:16.

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    Sorry Graham, but maximum endurance speed is lower than best range speed on every aircraft type I know of. This includes pistons and jets, fixed wing, and rotary. I've been measuring them for 40 years now. If you plot power required to sustain level flight versus airspeed, you always get a curve that starts at high power and low speed, drops to some minimum power at a higher speed, and then climbs with increasing speed (actually, with speed squared): the "bucket". That is basic physics. Best endurance speed is the low point on the curve, at the minimum power that will sustain level flight at any speed. Best range speed occurs at the intersection of a line through the (0,0) point and the power required curve.

    This is why Peter couldn't resolve the data he had for range at cruising speed, and endurance at minimum power speed, for the Sunderland. 14 hours at best endurance speed can not take you as far as fewer hours at the higher best range speed would take you. In addition, as you pointed out, you need to understand the assumptions behind any quoted range and endurance numbers (like payload, wind speed, reserves, etc.) to make sense of them.

    Come take some of my courses at International Test Pilots School and we can discuss this in more detail. And measure a few power required curves!

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