as well as littered with minefields, though not to the extent of the previous war.
Why not? I've have guessed Great War levels of deployment of any weapons systems extant in both wars would be the baseline minimum, not an unmatched maximum! Of course for one thing you could be accounting for time; the Great War ran from mid-1914 to late 1918, over 4 years, and so I suppose Allied minefields (I presume, leaving a little coastal corridor of the most stringent interpretation of Norway's neutral waters, which the Norwegians would have been obligated, to maintain claims of neutrality, to make some attempt to deter U-boats from taking refuge in themselves) simply got denser and more elaborate every year. OTL US Lend-Lease aid to the Soviets rose essentially linearly between the start of 1942 and a few months before VE day, a fact I often call attention to. So it could be that the Allies simply have not yet had time to match the 4 years in
peak densities of mines in this strait, especially since the British held off in the most aggressive minelaying there prior to Norway being invaded in April of the year before. Counting mid-April as the zero date for a comprehensive minefield to be undertaken, we've only had something like 16 complete months, some of which involved heavy distractions and major uncertainties as to whether control of Norway would hold. This versus over 50 or so by Armistice Day 1918.
But on the other hand, while I might not be aware of important increases in sophistication of WWII mines versus Great War ones (I am aware of none actually, and figure an early WWII mine and late 1918 one are pretty interchangeable) I figure mines are the kind of weapon system that a late 1930s-early war years industrial system like Britain's (not to mention the possibility of buying more from neutrals like the USA and Sweden) could churn out in gross numbers with higher productivity than peak wartime mobilization could do in the Great War.
Another reason besides simply not having time to lay the vast quantities eventually laid by late 1918 OTL would be if some alternative types of weapons systems make mines nearly obsolete--if we had some sort of ASB magic super-ASDIC that infallibly pinpointed every U-boat in the strait and tracked it for a hundred miles or so, it would be more cost effective to send an ASW task force to just stomp each one with depth charges, for instance. Aside from the fact that mines cost money and valuable war material resources to make, and are kind of hit or miss in their effectiveness, and mostly don't work at all (not commenting on failure rates here, assume those are zero; I mean relatively few mines are ever hit by enemy vessels) there is the nasty fact that postwar, the damn things remain a long term hazard to peaceful navigation and a major expensive effort must be made to sweep them up--an effort which inevitably misses some that haphazardly go off sinking innocent ships for decades to come. If one had an alternative to mines, that was more cost effective, we'd almost certainly prefer that!
However I think in 1941 the opposite is more the case. The highly sophisticated and effective ways of hunting down and sinking U-boats that would be state of the art and widely deployed OTL by 1944 or so here are experimental, when they have indeed even been proposed at all, and under development. With the relatively primitive methods shown here (of course leaps and bounds more advanced than 1918 practices, but still not nearly as impressive as the kind of thing coastal commands could do by the end of the war) we are driven rather toward the other end of the spectrum--good ASW assets are still in short supply. Whereas the big advantage over OTL is that the shortest width of the strait is controlled by the Allies on both sides; Norway is no longer a frugal, poor and low budged neutral leaving perforce a major hole in any attempted Allied barrages; on the contrary her west coast bristles with naval and aerial warcraft considerably beyond Norway's own most vigorous means, the British no doubt lavishing considerable investment in this task because costly as it is, the payoff is tremendous. If Fritz were entirely rational in fact, they'd give up on probing the north reach completely--so I have assumed anyway.
But recognizing that golden as the opportunity is to seal off this route completely, and even that the RN has somewhat more slack and therefore there ought to be ships available for this mission not OTL, underscored by the fact that if they can in fact completely cork up this strait so zero U-boats can get through, or even make the odds something like 50/50 they will sink a given U-boat attempting the passage, that the reduction in U-boats hunting in the northern waters will free up yet more ASW hulls surplus to reduced requirements in the broad North Atlantic--still, the ships and planes are finite in number, scarce at the start of the war. The fact that the Norwegian warships are a significant increment of the assets available underscores this point!
But then I think, we would want to substitute low quality, hit or miss weapons like mines churned out and laid in really massive quantity. Preserving certain relatively narrow channels for shipping, warships and transports, to pass through, where we concentrate our scarce ASW vessels, the almost continuous wall of mines, I was thinking, forces Fritz to either face the ships trying to slip through the openings, or face near certain death on some mine. No need to conceal where the mine barrages are; we want the KM to know it, and fear it.
OTL this was no option due to the Germans holding Norway; planes, coastal boats and U-boats, not to mention shore artillery, could repel Allied attempts to seal this passage off; Axis vessels, practically speaking U-boats later in the war, could simply hug the Norwegian coast and then break out along a broad front hard to patrol. I reasoned that with Norway an Ally, it would be far more feasible to block the U-boats
completely.
Well, apparently it ain't necessarily so; as late as November '41 a U-boat can seriously contemplate slipping past. I expect that to change both as various advanced technologies such as more sophisticated sonar and airborne radars come into play. I suppose when these were lacking, it was possible for the U-boats to surface at night, at least on dark nights, especially with overcast, and stand a good chance to fully charge their batteries before approaching passive barriers.
Come to think of it, obviously standard naval mines designed to catch surface ships would be a lot less effective against submarines, because the subs, approaching the field, could simply dive down to a depth where they would not trigger any mines floating near the surface--as long as the breadth of the field is not greater than their battery range, the mines would accomplish nothing. So presumably this was realized during the Great War and alternative mines were devised that park at greater depths; without very sophisticated undersea imaging, such as would be pretty nifty high tech today and certainly were not available in the 1940s, they would not see whether they were approaching such a submerged mine or not.
In addition to higher tech, as the war progresses, the Allies just keep accumulating assets until there are just lots of Coastal Command patrol planes and eventually there is no safe place for the U-boats to breathe; the breadth of the gauntlet would defeat them. If years must pass, meanwhile the Germans are going to develop stuff like snorkels (simply stealing it from the Dutch I believe) which still leave a radar signature to be picked up--but requiring far superior radars and still being pretty stealthy even then. Or the Walter scheme to power submarines with turbine engines (I believe, detail on these Walter engines has been hard for me to come by) oxidized by hydrogen peroxide for truly air-free submerged propulsion.
So, I have to guess you did your research and learned that even where the Allies had the luxury of setting up an antisubmarine gauntlet shore to shore, these merely caused some attrition but never turned into absolute uncrossable barriers. Silly me, I did thing exactly that could be accomplished, and assumed minefields would be the quick dirty way to achieve most of it, forcing subs to attempt much narrower passages where the Allied ASW is concentrated in force, eventually, as Allied resources get richer, with lighter screening ahead of and behind the main "wall" to give any U-boat captains intrepid and lucky enough to get through, either by braving random death in a minefield or running the active gauntlet in the open parts, nightmares of being caught anyway in more open water.
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One major pet interest of mine remains LTA, and in OTL WWII time frame, blimps. OTL the British (and French, and Italians) used smaller dirigibles, the British in fact inventing the term "blimp," for such auxiliary but important functions as coastal patrol. Now I have been assuming that Coastal Command (and thus the corresponding smaller numbers of planes with similar mission in Norwegian service, which actually make up the bulk of aircraft the Norwegians are manufacturing themselves) was totally up to the task, in conjunction with mine fields and seaborne destroyers and patrol boats, of blocking all U-boats by quite early after mostly clearing the invaders from Norway--the Germans hanging on in the south would not compromise this much I figured, though it is a great thing they are finally gone. OTL Britain did not revive her Great War blimp program at all.
But learning here that actually the great wall I assumed was totally blocking U-boats, or anyway with only a few occasional German subs getting through, is more the other way round, and most U-boats do get through at this point, I have to wonder, would not the British and Norwegians become a heck of a lot more interested in developing that option?
Airships, even small ones such as the K and L class ships the USN eventually operated in the hundreds in WWII, have certain inherent advantages in missions like this, especially in waters where the chance of an enemy air raid is remote to none. Their lift is quite respectable even by the standards of WWII airplanes--outclassed by the biggest transports, bombers and flying boats, but quite good versus more common smaller planes. They fly much slower and lower of course, but for a mission like looking for signs of enemy subs, these are virtues not vices. A major thing to consider is that generally, blimp flight is smooth and low stress, with few instances of large accelerations, relatively low vibration (well, give or take the proximity of radial engines right next to the gondola, but that is not worse than most WWII multiengine airplanes) and very expansive volumes are available for installations. For these reasons, advanced prototypes of new types of avionics were often pioneered on blimps--such as airborne radar, infrared systems, and magnetic anomaly detectors (MAD). Sonobuoys were part of the routine arsenal of late WWII USN blimps too.
In American coastal waters (and the USN eventually deployed airships in the Caribbean, down to northern Brazil, and ferried them across the Atlantic to North Africa to operate some even in the Mediterranean, as well as maintaining squadrons all along the CONUS coasts, from Massachusetts to Louisiana (offhand I can't recall a blimp base in Texas) and from San Diego to Tillimook, Oregon (again I am drawing a blank recalling any bases in Washington State) U-boat captains generally dived whenever they saw a blimp on the far horizon, knowing that if the "little airships" ever spotted them they could just pace them vectoring sub killers in. There are no acknowledged cases of these blimps ever destroying an enemy asset (there is some controversy about some claims, but official Naval ruling denies these cases) whereas once a U-boat did most certainly shoot down a pursuing blimp (it moved to attack but its Lewis machine gun jammed).
As noted, in the Great War the British improvised their own blimps, and such foes of large rigid airships as Winston Churchill did credit these little blimps with important accomplishments, of the same patrol, observe and deter type. They had therefore built some large hangars for them, in addition to other hangars such as the works at Pulham and Cardington for the big rigid airship programs. Cardington at least exists to this day, not sure about Pulham (it was the site IIRC where Barnes Wallis built R100 for Vickers in the late '20s and early '30s, unlike its more officially favored rival R101 R100 was nearly the same quite large size and was effective in the few missions, including a transAtlantic flight to Montreal, it was tasked with) lasting to 1941. At any rate--Cardington certainly existed, and could house a fair number of typical Goodyear K ships.
The USA not being in the war yet, there is some question as to whether Goodyear would be authorized to sell the British or Norwegians any blimps. In fact when the USA entered the war OTL, the Navy had just a handful of modern K and L ships (the latter were smaller, meant for training but pressed into service as patrol ships anyway, and were typical of the postwar advertising blimp in size)--they also had a half dozen or so interim semimodern ships built in the mid-30s for the US Army, which had until the later '30s the mission of defending US coasts! Goodyear's own in company small fleet of several advertising blimps rounded out the tiny numbers of these airships in operation--all were initially used for WWII coastal patrol until the Goodyear factories started cranking out new airships by the dozens and eventually, hundreds. Another troublesome point is that all these blimps were designed to be inflated with helium, which as of 1941 was a US monopoly, regulated by special Congressional law going back to WWI, under military control and reserved. Now I have read anecdotally that at least one L-type model was acquired postwar by a German operation which inflated it with hydrogen, and even that its flight crew included people who smoked tobacco on the job, and it flew a respectable number of hourse before being peacefully retired with no mishaps. So, especially if either Goodyear or Allied recipients modify the gondola for improved fireproofing, it seems possible that even without the USA releasing any helium, Britain and Norway can get started on inflating and operating several modified K or L type ships pretty much immediately upon delivery or soon after, even if they are forced to inflate them with hydrogen. If they do that, this will involve both cheaper operation (barring the risk of fire) and superior static lift, and leave open fairly conventional airship operational practices such as balancing water and sand ballast against venting hydrogen, which operators using helium had to avoid doing--not only was helium relatively expensive versus hydrogen (not that pure hydrogen was exactly cheap to be sure) it was also only available by being shipped in, whereas hydrogen can be manufactured in situ at any location with suitable plant and power available. (The Germans used to take finely ground iron, and blast it with suitably hot high pressure steam; the iron would pull the oxygen out of the water molecules leaving pure hydrogen gas with some residual water vapor, relatively easily filtered out; power therefore need not be electric, although the electrolysis process is obviously available too).
Aside from any qualms the US government might have about allowing the Allies access to Lend Lease helium, and associated logistic and handling plant installation issues, I am not sure what the attitude of Goodyear corporation would be if approached by an Anglo-Norwegian delegation to buy or license Goodyear designs. On the whole I suppose it would be favorable, probably. To be sure, between the wars Goodyear had corporate ties to the original Luftschifftbau Zeppelin company in Germany; Goodyear-Zeppelin corporation was spun off (still within the Goodyear corporate family though) to manufacture big rigid airships, and did make two (of an advanced design I love) for the USN, building a quite magnificent and elegantly streamlined gigantic hangar at Akron Ohio to do so. (A similar design was later built at Moffet Field for the USN, in Sunnyvale at the south end of the San Francisco Bay area, it is now the site of NASA Ames--also a number of the timber hangars built for the blimps during WWII were of this same streamlined design, more or less). Goodyear-Zeppelin was originally conceived, on the German side, as a life line because all German aircraft, especially Zeppelins, were banned by the Versailles Treaty and the Zeppelin works at Friedreichshafen on Lake Constance (Bodensee) were slated for demolition; at that point the American spinoff was seen as possibly the only refuge left for Zeppelin expertise to survive. In the event various stays of execution allowed Zeppelin to remain in operation in the 1920s and of course the company served the German Third Reich in the '30s--not everyone with equal enthusiasm; head Dr Hugo Eckener would often loudly denounce the Nazis as mere thugs and gangsters, and was stripped of his German citizenship and control of the company--but he did continue to work there, nor did the regime ever actually hunt him down. Anyway the early 1920s deal involved some 20 or so major Zeppelin designers emigrating to the USA to work for Goodyear-Zeppelin. The two companies had agreements of reciprocal licensing and other ties, still active into the later '30s Reich or no Reich. On the other hand, the chief of the German emigrant engineers, Dr Karl Arnstein, was actually despite his Germanic name of Austro-Hungarian birth, specifically from Bohemia, and his parents were Jews who had converted to Catholicism--so obviously he would have little sentiment for Hitler's regime on several counts, and in fact he renamed his children "Austen" in America. Arnstein is credited with primary design for the ZRS rigids USS Akron and Macon, and also is the primary name on the patent for the internal catenary curtain suspension blimp design I have been talking about as a "Goodyear blimp." But he was wearing a different hat than Goodyear-Zeppelin when he submitted that patent; GZ company existed to develop and operate big rigid airships, whereas the smaller pressure ships that Goodyear empire more often made in much larger numbers were under a different corporate division of the parent Goodyear company. I am not sure just how long Goodyear Zeppelin lasted on paper, into the late 1930s I believe, but meanwhile legally speaking the blimps were not made by GZ, though a lot of the same engineers worked for both, and I believe once WWII started, GZ was liquidated and its assets shifted over to Goodyear Aircraft Corporation, which made the blimps (as well as getting a contract for Vought Corsairs later in the war, and designing an upgrade of that naval fighter/attack plane, which got some test flights and a Naval designation FG, though the war ended before the Navy purchased any operational models).
So it is not the German born engineers, long supplemented by American ones working with them of course, I am thinking about here--not their chief, Arnstein, anyway. No, it is the presumably largely WASP Goodyear corporate directors I wonder about. In general many US corporations had rather dubious ties to Germany, in some cases with actually pro-Axis members of various boards or in executive positions, most often of course on the simple basis of profits from licensing deals going both ways with German firms. I'd worry that the special relationship with LZ in Germany might have biased Goodyear toward this lean a bit more than usual--surely many directors would be quite anti-Nazi but perhaps not all of them?
Certainly OTL once the USA entered the war, Goodyear was a major military contractor whose chief weapon system was aimed straight at defeating the Axis, Germany especially--blimps patrolled the US Pacific coast too against IJN subs, but it was obviously U-boats that were the worse overall threat and it was only in the European theater Goodyear blimps ever wound up advancing overseas, as noted via South America and Africa into the Mediterranean.
Another consideration against deploying blimps to close the North Sea route to U-boats would be the matter of hangars again, this time as being vulnerable to bombing. No American blimp hangars were under any but the remotest threat of Axis attacks; if we base hydrogen inflated K or L ships in Cardington however, might not the Luftwaffe make a special effort to surge in some bombers to hit that target? The Germans knew from their own Great War experience how vulnerable airship hangars can be to bombing, especially if the airships are using hydrogen for lift! Damage that would be only partial could turn into a general conflagration! Of course Cardington, and any other surviving big airship hangars in Britain, would have been designed to minimize fire danger, since all British airships were lifted by hydrogen. I was thinking it would not be too difficult to throw up a big timber hangar in Norway, given the abundance of timber in that country, but of course this too would be vulnerable to a major Luftwaffe initiative unless placed pretty damn far north, say in Narvik or even beyond.
If Allied blimp use converts back to helium lift despite the drawbacks (and OTL the USN was certainly able to operate far from CONUS on that basis after all). this danger is somewhat mitigated but not eliminated. I suppose one solution would be to develop a major hangar complex in northern Ireland, and then deploy blimps from there to expeditionary masts in east Scotland and in Norway, perhaps with a Norwegian hangar in Narvik--or if judged safe enough, Trondheim. Blimps most certainly are capable of very long ranges and endurance! Another option is for the Allies to procure or modify some other type of ship into a seagoing airship tender such as the USS Patoka; blimps could moor to it, and be refueled and otherwise gunned up, perhaps even exchanging crews, for it to then take off and fly another patrol of some days.
At 800 meters altitude, doing the math in my head I think the line of sight distance to the horizon is 100 kilometers, close to a full degree of circumference. Now at the extreme range this is not worth much to be sure. (A typical GAC blimp could rise a lot higher; the two main ballonets plus sidesaddle "pannier" ballonets had capacity of a quarter the whole envelope volume and so it could rise to an altitude where air density is 3/4 that of sea level without venting helium, some 3 kilometers or 10,000 feet--though I think trim considerations making it undesirable to empty the air ballonets would make a practical ceiling somewhat lower. But much of the benefit of using a blimp for coastal patrol is that it flies very low as well as slow (some 40 knots cruising speed, being able to surge up to about 60 or perhaps, with souped up engines and redlining everything, somewhat faster--the issue is not power so much as structural risks at high airspeeds. Flying low and slow, endurance is incredibly long, and fuel consumption quite frugal. Low means very close scrutiny of nearby waters and slow means little disturbance of close observation by zipping past difficult to observe U-boats). The long line of sight is much longer with typical airplanes of the era of course, but where the blimp might really shine is if we install very powerful radar in it. A large radar set at high power could perhaps sweep a very wide disk of ocean for even subtle U-boat signatures, then if seeing any the airship can come very close. Now German U-boats had deck guns, and if the blimps must use hydrogen they might be terribly vulnerable if they stick their noses in too close, but vice versa a sub surfacing to attempt to shoot down the blimp would give away its position; it might be a trade of one blimp for one submarine. But that's the worst case; at its attainable airspeeds the blimp can run from a WWII submarine after all.
Thinking that good radar coverage might be limited to say 30 nautical miles or so in radius, a dozen or so radar equipped K ships might be able to maintain constant surveillance, day and night, of a solid swathe 60 NM across and stretching from the Scottish coast to Bergen. This is not quite the perfect infallible U-boat finder I mentioned as an ASB ideal up post, but it comes scarily close for the KM sub crews!
I think, given the revelation that conventional ASW ships and mines are not cutting it, that the Admiralty or RAF might figure this vulnerability out early on 1940, and turn to approaching Goodyear Aircraft Corporation, either hoping for US release of helium for their regular operation, or a reasonable set of modifications to enable fairly safe operations with hydrogen, and beginning early in 1941 start operating increasing numbers of big blimps, to tighten up the seal on the Scotland-Bergen barrier line, and also to range far north of that line to pick up any U-boats that got through, and perhaps, if Luftwaffe strafing attacks can be held back, south of the line to winnow out some of the U-boats contemplating running through that line and deter them from trying it. If hangars in east Scotland and Bergen are too vulnerable, the long range of airships enables them to operate far south or east of their main bases, and IIRC, stay on patrol day and night for days at a time--the crews were large enough for multishift operations of that kind to be feasible.
The advantage over faster and higher flying fixed wing aircraft is as noted that the gentle conditions in the airship enable fussy, tempermental advanced gear prototypes, or very high power versions of more conventional equipment, deployed hard against a surface pretty near by and quite competitively with any land plane.
