The problem was with the culture of the US higher command levels. Pre war it was riven with political infighting and they simply ignored the facts in front of them. As I've pointed out the RAF went over to the US and demonstrated their ground controlled intercept system. Despite having seen how well it worked they turned up their noses at it. The problems with the US command structure were well known within the US military, it was just infighting meant they did nothing about it until forced by the harsh realities of war. This is the problem which needs to be addressed.
As a radar Chain Home was amazingly primitive already in 1941 or even 1939. As you note, what made CH an effective force multiplier in the interception mission was integration with the command structure. The spotters (women, during the war, I believe) had a hotline phone to Fighter Command; FC had practiced integration and had confidence in it, and IIRC a voice over radio (these, during wartime mobilization anyway, I am more certain were generally women) would issue instructions to the interceptors to vector them at the targets. Elementary stuff, but as you note nobody but the British were doing this. It was more than just installing radar kit, it was getting the command structure to trust the newfangled equipment against "not invented here" prejudice. Contrast the situation in Hawaii in the Pearl Harbor attack; the Army radar team was experimental. The radar itself was vastly superior to CH, but the team was not even authorized to be working on a Sunday. They spotted a mysterious, unlogged formation and called HQ, and the officer in charge there supposed it was probably some incoming B-17s being deployed and angrily reprimanded the radar chief for daring to waste taxpayer money and to stand down and report to barracks immediately. This story is from memory but I am pretty sure the gist of it is correct.
As a side note LTA wank, I've wondered if the Navy had followed through on their plans for big rigid airships of the Akron-Macon type (presumably with some extensions of lift capacity and other nifty modifications by 1941) and had a hangar as well as mast in Hawaii, whether some rigid operating with a new radar set aboard (airborne radar is a whole different thing, but a 250 meter long or longer airship can lift a lot of equipment, and with a lot more elbow room for bulky and power and cooling hungry Mark 1 experimental kit, also in much more stable, shock free conditions allowing for fragility--in fact OTL quite a lot of advanced gear such as radar, navigation systems, magnetic anomaly detectors, later infrared scanners, were first tested out on blimps before models that fit into airplanes and helicopters could be devised) operates offshore, and the Navy airship being better integrated into Naval command, the warning is taken more seriously and checked on. In principle we might not need an actual rigid, but I think if the forces that sank the USN rigid scheme OTL prevail (and I admit the Navy had reasons to give up on it in the mid-30s) there wouldn't be a lot more support for blimps than OTL either, whereas the really big blimps that might have served for this were not developed (the M ships aka "Mike") until late in the war.
Speaking of blimps and coastal patrol in general, that was yet another Not Invented Here thing the Navy infamously spurned OTL. The Army had had the mission of coastal defense coming out of the '20s until the mid-30's; they had a legacy investment in coastal artillery and the wacky notion that B-17s could sink ships bombing from high altitude. In fact the transition from the rather primitive WWI legacy blimp design with draggy open external rigging over the hull to suspend a gondola below happened largely to develop the early to mid '30s Army patrol blimps--Karl Arnstein and some other guy, another of the Germans (well, Arnstein was actually a Czech of ethnically Jewish background though his family had converted to Catholicism and Germanized in Austria-Hungary) sent over from Zeppelin company to form Goodyear-Zeppelin's design team core, had his name on the patent for internal curtain suspension such as modern blimps use, and the wartime L, K and M models for the Navy used these, as did the transitional Army TC ships the Navy inherited when the Army was stripped of coastal defense mission, around the same time the Navy's rigid program was put into suspension and ultimately shut down.
In OTL wartime, the blimps based mostly at rapidly constructed gigantic timber hangars along the coasts (and later operating in the Caribbean, northern Brazil, and even on an expeditionary basis in the Mediterranean, self ferrying over from Brazil to West Africa and thence up the African coast) would go out to spot for U-boats. They never were credited with actually sinking a U-boat themselves, but as a general rule, the sub commanders quite understood their danger whenever a blimp was in line of sight and went down to hide, which was not always successful. (Then Doenitz ordered them to be more aggressive, they had deck guns after all, and at least one blimp was shot down when its own Lewis gun jammed). Overall the blimps, while not covered in sub-killing direct glory, still were a very effective form of ASW, often locating a sub for other assets to sink, and generally reducing their effectiveness by immobilizing them. Toward the end of the war the Navy had a hundred or so airborne and operational, mostly the K model. (The L-ships were smaller, and typically the model operated as commercial blimps postwar, including the fleet of Goodyear's own corporate flag-showing little fleet, also used as trainers in the war but also operational patrol ships).
Early in the war however, the Navy had almost none of these blimps, essentially all but a handful were built as wartime expedients, in truckload lots. Early coastal patrols involved models taken over from Goodyear's civil fleet that had a guy with a rifle aboard as its whole armament. But again the mission is not to wipe out the entire German and Japanese sub fleet but to spot intruders so someone else gets the glory of trying to sink them.
So--as a general thing, the Navy had the coastal defense mission, and by extension and with even greater logic, that of escorting convoys.
But the Navy brass had no stomach or interest for such a plebeian, inglorious role as shepherding grubby commerce up and down the American coasts and guarding convoys. They took no action and the outcome was the "Second Happy Time" for U-boats stationed on the west side of the Atlantic bagging ship after ship. Belatedly and grudgingly the brass came around to the idea that protecting this commerce was in fact a vital Navy mission.
So broadly speaking, the tendency of military strategic planners to fight the last war, and the glorious war they'd like rather than the inglorious hell war that is the winning strategy, comes under the rubric of my remarks on the inappropriateness of premature massive buildups of equipment sure to become obsolete fast, versus reserving the productive potential for making what is really needed when it is needed. It is not the same thing but it is the same kind of thing, relating to the inability of people to forecast exactly what the situation will be when war actually comes, as well as systemic biases that tend to arbitrarily rule things or strategies "good" based on theory and unrealistic test exercises--as with the poor performance of US torpedoes, because of politics shielding the Navy arsenal producing them from realistic accountability. In theory we can counsel perfection and shake our heads at political interference and tunnel vision, but realistically these things we shall have with us under any regime.
Again, it seems a counsel of perfection to ask for perfect foresight. Planners like Patton had a fair idea what they wanted and I suppose his notions of what tankers should learn to prepare for were sound enough; then he had to run practice exercises with plywood cutouts mounted on cars and sticks for guns. The Army Air Force was quite sure they could "put a bomb in a pickle barrel" and sink ships with high altitude bomb runs from B-17s, using the vaunted Norden Bombsight.
No battle plan survives contact with the enemy, and egregious oversights prior to the fighting started seems to just be par for the course.
