I recently watched this Roger Corman WWII film, and thought I'd tell you about it.
This is one of a trio of movies that Corman made in Puerto Rico for tax purposes. Joel Rapp and his friends put up some of the financing, and he was the director; he had acquired the rights to a short story, Expect the Vandals, by not-yet-famous Philip Roth.
I have the Roger Corman Puerto Rico Trilogy DVD set, and it includes a commentary track with director Joel Rapp (with Fred Olen Ray). It's fun to listen to, though he doesn't spend much time discussing the movie we're watching! 
(Years ago, Fred Olen Ray wanted to see this film, and ended up buying a theater copy that he had to put on a projector! This DVD uses the print that Fred Olen Ray saved.)
Roger made low-budget movies, and the important thing about the screenplay is that it primarily involved two U.S. soldiers on a Japanese-held island – that could be filmed inexpensively!
Joel was serious about this movie, however, and hoped it could be marketed through the "art house" theaters eventually.
The star is Richard Devon, who had previously appeared in several Corman films, including as the star of War of the Satellites. He plays soldier Moe.
Ron Kennedy (AKA Ron Gans) is his co-star; he was a friend of the director, and helped finance the picture in order to get the role of soldier Ken. (He's better remembered today for his voice work.)
There's some uncertainty about how the movie got its final 'introduction' scenes. When the completed movie was shown to the critics, it was not received well enough to justify a release to the art houses. Corman therefore needed to make some changes to make the film viable for the drive-in theater market. Then, a few years later, television came along, and scenes needed to be added to make the film into a standard length for television. So, additional material was filmed in California. The director was not happy with the changes.
So the film became 'Battle for Blood Island' to help it sell at the drive-ins (it was on a double-bill with Ski Troop Attack). And since there was no 'battle' in the original movie, new scenes were added depicting the attempted U.S. landing on the Japanese-held island. The idea is that the American invaders are fouled up by an unknown reef, allowing the Japanese defenders (played by Puerto Rican actors) to kill most of them.
The two survivors are Moe (an older, Jewish soldier) and Ken (a young man paralyzed by a wound). Moe saves Ken and, undetected, they make their home in a cave on the island. Ken is entirely dependent on Moe, who scouts the island to find out where the Japanese camp is.
The movie is essentially a story about how Moe and Ken struggle to survive, how Ken deals with depression, and how they almost go crazy.
There's an odd twist about halfway through the movie, when you think the story is going one direction, and then it veers off into something else, and you're not sure if it's going to be sci-fi, fantasy, mental illness, or what.
Roger and Joel both make brief appearances as U.S. soldiers.
The acting is adequate. Richard Devon has an acting style which some like and some hate. Ron Kennedy handles his role well.
The movie is slow-paced, and the last half of the movie dragged for me.
It's not bad, though. More of a psychological movie than a war movie.
About an hour long. Black-and-white.
IMDB: https://www.imdb.com/title/tt0168492
If you're looking for scenario ideas, the premise of two soldiers stranded on a Japanese-held island could certainly make an interesting skirmish campaign.
