A 1975 Japanese thriller titled “Bullet Train,” about a high-speed passenger train with a bomb on board, one that will explode if the train slows beyond a triggered speed, inspired the bomb-on-a-bus thriller “Speed,” its sequel and lots of imitators.

It was a the biggest Japanese disaster pic of its era, excluding movies starring a giant monster from beneath the atom-bomb-tested sea. So of course it inspired a sequel. It just took 50 years to get around to doing it.

“Bullet Train Explosion” references the original film’s “incident” as it hurls a cast of cast of dozens if not hundreds and modern CGI effects at that still-somewhat-plausible scenario- – a murderous bomber holds both the train and the entire country hostage as the sleek, streamlined locomotive and passenger cars hurtle towards their doom.

There are suspenseful stretches and vigorous “work the problem” exercises blended into ludicrous twists and the odd dash of Bugs Bunny Physics in this self-serious thriller built on classic disaster movie bones.

We meet the vast array of characters — uniformed personnel of the Hayabusa 60 that sets out from remote Aomori to Tokyo, technicians of the railroad’s control center, the suits at Tokyo HQ, and select passengers from the 300+ souls riding the rails this fateful day.

Tyuyoshi Kusanagi of “Doomsday: The Sinking of Japan” stars as white-gloved conductor Takaichi, whose attention to detail and crisp salutes aren’t sinking in fast enough with his subordinate, Fujii (Hanata Hosoda).

“This is is a serious job, you know,” he scolds in subtitled Japanese, or dubbed into English.

The train’s driver is a just-as-meticulous young woman, Mastumoto (Non) who sits in the cockpit alone, reciting her various safety and start-up protocols aloud as they set off.

A huge high school field trip, a scandalized politician (Machiko Ono), an “unemployed rich man” influencer (Jun Kaname) and a sketchy guy with a bulky bag and wearing a respiratory mask are among the paying passengers.

The train gets under way. The bomber phones HQ with threats and a demand — 100 billion yen (702 million in dollars, a figure tariff-shrinking by the hour). How serious is this bomber? A freight train is blown up with an identical bomb to get the point.

As the people in charge scramble to respond, politics interferes and the passengers are abruptly made aware of their plight. Some panic, cast blame and insult the “Sugar Mama” politoc. And one takes matters into his own hands. The ransomer wants “all of Japan” to pitch on this? Fine. Let’s set up a Go Fund Me page. All those kids on “Insta” spread the word.

Meanwhile, an audacious “rescue plan” is cooked up at HQ. How do you defuse a bomb you haven’t located on a fast moving train? What might plan B be?

One of the cute touches here is somewhat jarring if this is the way these trains, which have been around since the early ’60s, are operated. Officials communicaste with land lines with flashing red lights, a situation room features models and ancient and simple what-train-is-where display board and wind-up stopwatches are used to time speeds and operations suggest that the world’s onetime digital electronics leader is still running its rail network in an analog world.

“Tradition?” No money for upgrades? Union rules? It is to laugh. And perhaps that’s meant to be a joke, as the film itself is so old fashioned as to be creaky.

The picture’s turn towards “Give me a break” nonsense roars in with the third act. Before that, we’re treated to a few too many scenes of cool-headed professionals performing their professional duty professionally.

But the odd moving moment, acknowledgement of “duty” and comically absurd throw-down over what decision should be made and by whom enlivens the proceedings, even if it doesn’t come close to overwhelming the intentional or unintentional silliness of stiff actors playing all this so very seriously.

Rating: TV-14, violence, blood

Cast: Tsuyoshi Kusanagi, Non, Machiko Ono, Daisuke Kuroda,
Jun Kaname, many others

Credits: Directed by Shinji Hiruchi, scripted by Kazuhiro Nakagawa and Norichika Ôba. A Netflix release.

Running time: 2:14