Ok, so this is a sensitive subject for a variety of reasons, not the last of which the fact that Americans in particular have such a short attention span when it comes to history in general, and in geostrategy in particular. Nevertheless, you asked genuinely for response so I am giving it.

To much of the US and even the UK, have this idea of the monarchy as vestigle forms of the state required only for ceremonious pomp and ceremony, but I would venture to say this is not much more than a well placed propaganda myth. I say this because understanding the history of relations between the US and the UK, I propose, can never be understood properly until one gets past this first point.

To review a timeline of relations between the two countries, allow me to refresh your memory of times in which then GB opposed the US. Of course, the revolutionary war, and the war of 1812 with the burning of the whitehouse and the capitol, but the one I feel most misunderstood and mistaught in schools is the civil war, in which Britain openly sponsored the confederate states in an effort to undermine it's traditional enemy. After this is where the "mainstream history" goes off the rails and, due to WW1/2, pretends there was little animosty remaining due to the great alliance needed to defeat the enemy.

King Edward VII, often mistold in the histories as a gallavanting playboy, was actually instrumental in establishing the encircling alliances leading up to the first (and hence the second) world war. Through Sir Edward Grey (Yes, the tea), who controlled Edward House, Woodrow Wilson was pushed into the war despite the fact he had campaigned on not doing so. Of course after WW1 the issue of naval supremecy was a primary pain for both, which is why in naval parlance the Paris Peace conference is referred to as the Naval Battle of Paris. Admiral Benson of the US, during a meeting in which a British Sea Lord was found proding a secretary for information about the US's postwar naval building plans, said of Britains desire to maintain naval supremecy; “[...]it will mean but one thing[...] war between Great Britain and the United States.”[1] Of course, you mention war plan red, but the mistake is to dismiss it as a dusty old plan never intended for use. It was very much part of a real potential response to the entangled alliances developing. It was worked on up to 1936, by none other than Douglass McArthur.

As for WW2, the propaganda primarily centerred around anglo-american unity centered on the Atlantic Charter and it's four freedoms, even though Churchill later said the four freedoms did not apply to the British Empire, or even outside of Europe. This is where it gets more complicated, because it's mostly all about old war plan maps and the military pushback of the US against plans laid out by the UK. Only a handful of generals were able to comprehend the game GB was playing at manipulating how bloody the pacific campaign would be in order to influence the post war balance of power. McArthur was one of them, and his initial pushback against the proposed Brisbane line was only the first in many such political-strategic military moves to counter the traps set by Churchill. This pushback is what moved the lines of battle into New Guinea and the Owen Stanely mountain range. I come from a long line of military men, and a great uncle of mine was wounded on Guadalcanal and later died on the second push of Iwo Jima. Gudalcanal was an essential defensive victory which helped in reversing the Japanese "invincibility" by defeating them in the Battle of the Coral Sea. McArthur also avoided Churchills plan of full frontal assault of each fortified island by conducting leapfrogging instead, gaining control of lightly held islands to establish air bases and supply routes, which allowed him to get all the way to Tokyo with less than 90,000 casualties. The point of me droning on about this is that Churchill was most defenitly not a true ally of the United States, and the hero worship of him I see in modern media disgusts me. If he had his way the US would have bled out people for many more years than happened, and he was a scoundrel for it and more.

After WW2, the British plans for Pacific balance of power were shattered because of this, which is why they supported Mao Tse-tung inssurection as a counter against the American friendly Chiang Kai-Shek’ nationalists and their allies in the inner areas that were against the British colonialism. In order to reinforce this move, they used the Harriman (from which the Bush dynasty emerged) faction, including General Marshall and eventually Henry Kissinger, internally in the US against those resisting it. One of the telling moves was that after Mao's march in 49, the British were extremely quick to recognize his government and supply him with strategic goods through Hong Kong. As a matter of fact my old Marine Corps unit to this day still has symbols on the unit logo from it's China Marines days. To further restore the balance, they entangled the US in Korea, and it was McArthurs brilliance that created victory with inferior numbers and supplies, stunning the British, as they expected a different outcome. Since that play had backfired, the triple-agents in waiting were activated (though some had been used already during Korea), including Kim Philby, Guy Burges, Donald Mcclean, Anthony Blunt, Lester Pearson, and Victor Rothschild. They were triples because at first glance they were British agents, at the second layer they were recruited by the KGB (the Cambridge 6, yes, that's right, 6, not 5) but behind it all, they were ultimately loyal to the British monarchy. Plausible deniability you see. Eventually, the Harriman faction pushed Truman to finally get rid of McArthur for being such a pain in the imperialsts ass.

Now we get to Vietnam. After Diems assasination, the best option for the US would have been to stay out of that war, but a Saigon military advisor by the name of Sir Robert Thompson was at the time billed as the number one expert in counterinsurgency (shades of Patreaus anyone?), and later Robert Macnamaras book, the Pentagon Papers, et al, showed that it was his influence that was used to get LB Johnson to "take the plunge" in Vietnam once JFK was no longer around to veto it. It was Thompson who pushed for COIN operations in the south via US divisions in the Mekong delta doing nation building, despite the fact that the south Vietnamese defense minister had a superior plan in cutting off the Ho Chi Minh in the north near Laos with just a few US divisions by building a wall, and if the NVA tried to amass and attack, an amphibious assault from the rear would destroy them, and the nation building in the south would be left up to the Vietnamese themselves.

[1]https://www.usnwc.edu/getattachment/5a2b52ff-831d-446b-b41f-...