The past is a foreign country; they do things differently there.
Introduction
No comprehensive discussion of Isekai as a genre is complete without mention of Don Taylor's seminal 1980 film, The Final Countdown, concerning the USS Nimitz's journey through time and space to the eve of World War Two (for the Americans, anyway). As discussed in other essays by American Oneironautics, most notably "The Imperialism of Isekai", the genre of Isekai is broad, and encompasses many works, and types of works. That essay defines Isekai, so I will not do so here at length. Instead, I will briefly summarize the key characteristics identified in the aforementioned work.
Most prominently, isekai anime features a predominantly male protagonist who is transported quite by accident to another world, wherein he is afforded some technological advantage over the natives of this different world, either by his modern knowledge or by virtue of some doodad he happened to bring with him. This protagonist further begins "a program of cultural or technological conversion in the new world", that is to say, he tries to make the new world more like the old world. Lastly, the protagonist "acts as a savior/protector to a primarily female native population."
As noted in "The Imperialism of Isekai", imperialism and imperialist sentiment are endemic to the genre, and almost necessarily accompany any "accidental travel" scenario in which a notable power imbalance exists. Thus, American Oneironautcs contends that another key element of isekai artwork is a troublingly pro-imperialist attitude, however unintentional or subtle it may be.
It would be absurd to suggest that The Final Countdown, an American live-action film, is anime, so that argument will be set aside and revisited in another essay. Instead this essay will focus on the aspects of The Final Countdown which qualify it as isekai, focusing on the qualities of the genre, and not the medium.
Points of Conformity
First, the most obvious. The Final Countdown is unquestionably an "accidental travel" film, as the inciting incident is the passage of the USS Nimitz with her crew, complement, and an airborne F-8 Crusader through a literal time vortex to December 6th, 1941. The crew soon discover their predicament, and the incredible position it puts them in. They have both knowledge of the imminent attack on Pearl Harbor, and the weapons to do something about it. In fact, the first third of the film is replete with carrier deck action: launch, recovery, fuel and ammunition movement; these are things I call "Carrier Porn" and also include shots of the Nimitz's water line as she cuts through the Pacific. Segments like this are scattered across the film, and lend the whole work the air of a recruiting film.
Isekai are almost invariably imperialist by nature. To satisfy the requirements laid out for membership in the genre, a work must feature an "advanced" culture encroaching on another "less advanced" culture. The Final Countdown certainly fits the bill, as a Nimitz-class carrier with its complement of jet aircraft is vastly superior to anything the Imperial Japanese Navy could muster in 1941. Add in the existing US Navy at the time, and the IJN stands less of a chance than it did anyway (read: not that much in the long run, given the massive resource and manufacturing advantage of the United States).
The audience's first taste of this imperialist ultraviolence is a pitched air battle: two F-14 Tomcats intercept a pair of Mitsubishi A6M Zero's. One Zero is torn up by the lead Tomcat's 20mm cannon, while an AIM-9 Sidewinder leaps off the rails of the Number-2 jet to fireball the second Zero. All of this is filmed with real aircraft, and the full support of the US Navy.
Immediately following, S-3 Viking helicopters from Nimitz rescue a fictional US Senator, Chapman, and his aide Laurel (and her dog Charlie) after their yacht was sunk by the since-splashed Zero's. They also rescue one of the Japanese pilots, who later overpowers a Marine and takes Laurel hostage. Here we can focus on one of our protagonists, the Commander of Nimitz's Air Group, Commander Owens. CDR Owens, who oversaw the helicopter rescue, again comes to Laurel's aid, distracting the Japanese pilot and allowing the Marines to shoot him down.
On to the program of conversion. It is decided that the Nimitz will intercept the Imperial Japanese Navy before it can strike Pearl. More carrier porn, as a strike group is assembled, and CDR Owens prepares to drop the Senator and Laurel on a deserted island (so as to keep them safe from the expected chaos at Pearl and aboard Nimitz). Nimitz launches her aircraft, tight formations of modern jet fighters juxtaposed against a sky full of Zero's.
Subverting the Genre
However, this all turns out to be moot; the time vortex returns just in time to give me the worst case of cinematic blue balls I've ever experienced. Imperialism or not, my dumb ass thought I was going to see large-scale air combat between F-14s and A6Ms, something which I have to this day been denied, and for which I can never forgive Don Taylor.
However.
Taylor, in my view, has successfully subverted the isekai genre in several major ways. First in the relationships between the oppressor and the oppressed in the imperialist paradigm, second in the actual events of the plot, or lack thereof, as the case may be.
Unlike most isekai, wherein the "different world" is completely alien to the transported protagonist, The Final Countdown features protagonists transported to a world they may very well have lived through. Kirk Douglas was 64 in 1980, meaning that his character, Captain Yellend, would have been alive and likely serving in the US Navy in 1941 (at age 25), a fact likely also applicable to some of the officers and senior enlisted men on Nimitz, and which was jarringly and frustratingly ignored almost entirely by the film and its makers.
Further, remember CDR Owens and his Gilligan's Island trip? Well, the Senator fireballed an S-3 with a stolen flare gun, killing himself and a few Naval Aviators, and stranding Laurel and Owens on the island. Owens is left behind in 1941, but in a bizarre-yet-completely-predictable twist greets Nimitz upon her return to 1980 Pearl Harbor.
The Final Countdown may be unique among isekai, in that its protagonists conduct a sort of imperialism against their own world. Or, they attempt to conduct a sort of imperialism against their own world. In the frustrating climax of the film, this is thwarted by the same unexplained time vortex that initiated this predicament, and leaves us all wondering what might have been. With minor exceptions, the "imperialists" failed to imperialize and nothing of substance was changed in the "new world", and so Taylor is partly absolved of promoting imperialism, but only partly (he still took the Navy's money).