Pop quiz: you're a part of the modern armed forces in peacetime on routine manoeuvres and you find yourself thrown back in time with a chance to change history. What do you do? Well, if you're a Hollywood studio, you change the Japanese G.I.s in G.I. Samurai (aka Timeslip) to the crew of an American aircraft carrier, have them debate stopping the attack on Pearl Harbour for 90 minutes and then go home and hope that no-one reminds you that Japan did it first and with more balls in 1979 with this Sonny Chiba movie. But unlike its Hollywood counterpart The Final Countdown, this sees its premise through: thrown back 400 years into the Japanese feudal wars, its peacetime soldiers decide that their best hope of getting back lies in provoking history by trying to change it by joining with a warlord to conquer the country - cue lots of tank and helicopter vs. samurai action, including a very impressive unrelenting 25 minute battle sequence featuring a cast of thousands inflicting serious damage on each other. And yes, there are decapitations.
Of course, things don't go as planned, and even superior firepower doesn't stand up as well as hoped to thousands of soldiers. Even before that, the soldiers are falling out with each other into those who want to go home, those who want to go to war and those who want to rape and pillage for the Hell of it.
Impressively directed and surprisingly well thought through, the soft rock and country and western songs are sometimes a distraction, especially when they feature English lyrics sung by Japanese singers who audibly can't pronounce the words let alone speak the language, but it's a forgivable flaw in a surprisingly good sci-fi actioner.