Gonna bump this for you, and say that I think it is not Japanese, because I don’t see any recognizable kana in it. But it’s hand-written and pretty blurry on top of that, so I’m not certain. And because of that, I can only recognize a few characters. I think it starts out “Greater China” and then China is mentioned again later.
Since the movie is supposed to include Japanese people in the story but apparently no Chinese people, maybe this was represented in the movie as being in Japanese, but if so I’m pretty sure they got it wrong.
Roddy
It’s traditional Chinese. Too hard for me to read as it’s really blurry.
I’m not a China Guy, but those characters seem to have more the ‘look’ of simplified chinese. Just curious if you meant ‘old style’ chinese per se, or Chinese vs Japanese
Those aren’t simplified characters, and couldn’t be as they were invented in the mid 1950s. “Republic of China” is written as 大中華民國 and not 大中华民国. It looks like Chinese but may be Japanese written all in kanji; there are too many blurry characters to be able to make out the text. I’m seeing the aforementioned “Republic of China” mentioned a few times, as well as “border” (國境), “territory” (領土), “military secret” (軍機).
The second line reading right to left (or the first line after the guy’s right thumb) says 大中華民國 or “Great Chinese Republic,” and the last line at the very left looks likes it’s got a date of 1936 (中華民國廿五年). I also spot the word 軍, “military” or “soldier” in several places including in the title of the document (the characters above the holder’s right thumb). The rest is really hard to make out, though. At a guess, I’d say it’s some kind of military pass or requisition form.
i can also see mention of “… if needs be … uncover(?) traitors, local and abroad …”
Maybe it’s Man’yougana 
ETA: Man'yōgana - Wikipedia (Man’yougana is ancient Japanese writing. It’s essentially a subset of Chinese characters used purely phonetically, it ultimately became corrupted into what we call hiragana and katakana today)
Thanks, all. Next time it’s on I’ll snag a clearer copy.
Taiwanese wife says that the second character of the title is “権” (or rather the traditional character for it) or “authority” making the first two words of the title "military authority (something). There is also “military command” in there and I think I see a 任状 or at least 状 on the end of the second line, which would be some sort of letter authorizing the bearer of the letter to some sort of authority.
Between my mom and I, this is what we’re guessing…
(ETA: It’s written here left to right, top to bottom, but in the actual letter it’s written top to bottom, right to left)
軍糧_ _ _
大中華民國為
頒給軍糧委任狀
中華民國領士主糧
總司令如有需要特准予行
於國境內外並于全糧沒收
事_資驅出內外漢奸_金
中華民國廿五年 _月_日
It doesn’t make complete sense grammatically, but it seems to be a letter granting a Commander in Chief right of passage through all its territories in order to requisition wartime rations as necessary. Something like… “commander, if you need, you may go as you please and take our rations”?
We’re not sure if it’s an archaic dialect of some sort or just nonsense mixed in with a few actual phrases.
The date indicated at the very left is in Minguo years, and converted to the Gregorian calendar as Koxinga did, that’s roughly the period of the Second Sino-Japanese War. During that time, the Republic of China (中華民國, or what is now known as Taiwan) still controlled the mainland and was at war with the Japanese.
This may have been an actual letter from that era or it may have just been a movie prop made to look like one. It’s hard to dismiss it as a fake altogether because certain elements seem real enough (some phrases are legit, the red square stamp on the left hand side looks a lot like an actual seal, such as found in this letter, etc.).
But what that has to do with the movie – which according to Wikipedia is about shipwrecked American and Japanese prisoners of war struggling to survive on some island – I have no idea.
Well, here we are ten years later, and somewhere along the way I saw this letter again. I would like to thank the people who attempted to translate the blurry screen cap. I’ll resupply one, since the one in the OP is long gone.
As it turned out, guess what. . .
A) This letter is reused from another movie Never So Few (1959), and
B) The translation rendered in that movie is actually pretty close to what was attempted above.
British actor Richard Johnson, playing Capt. Danny DeMortimer, says it’s a warrant from the Chungking government revealing that:
The bearer is charged and entrusted to preserve the territorial integrity of China by preventive measures if necessary within or beyond the geographical bounds of the Republic. The bearer is further authorized to confiscate all military materiele, to deal with all invaders, and to rout out all traitors, domestic or foreign.
Coincidentally or not, both movies started Frank Sinatra.