Tarzan and the Foreign Legion by Edgar Rice Burroughs (1947)
First off, the book starts off with a note from the author that at the time he decided on novel's setting he was woefully ignorant about Sumatra and the local library in Honolulu had no books on the subject. (Woeful ignorance about a location had never stopped Burroughs before.) Nonetheless, Burroughs relied on the knowledge of a humber of persons whom he then thanked. The important thing -- to me, at least -- was that Burroughs dated the note September 11, 1944, indicating that the book was written during the height of the war in the Pacific even though it was published several years after the war ended.
It also should be noted that Tarzan and the Foreign Legion was the 22nd and last Tarzan novel published during Burroughs' lifetime. The jungle swinger had been having adventures since 1912 and was one of the mosr popular characters in world.
So...Sumatra. Well a jungle is a jungle and Burroughs had used the Africa locale many times as Tarzan fought thee enemy during the first world war. RAF Colonel John Clayton was aboard an American B-24 for a reconnaisance and photographic mission over the Japanese-held island when the plane was struck by a Japanese Zero. The plane's pilot, Captain Jerry (a truly noble name, that) Lucas tries to guide the plane from the anti-aircraft guns along the islands shore. Knowing they were to crash in the jungle, Jerry orders everyone to parachute off the plane, himself being the last to jump. Once on the ground, Clayton shucks his clothes, fashions a loincloth from part of his parachute, and takes to the trees in search of survivors.
At least three of the plane's crew have survived: the nobly-named Jerry, hailing from Oklahoma City, S/Sgt. Joe Bubonovitch, a college-educated zoologist from Brooklyn, and S/Sgt. Tony Rosetti, a poorly educated man from the streets of Chicago. Bubonovich and Rosetti, besides being fearless fighters and the best of friends, provide the comic relief. Tarzan leads the crew away from the flaming wreckage to begin a long trek through enemy territory toward the shore where they hope to find a boat and sail to Australia. Along the way, they rescue Corrie van der Meer, the eightee-year-old daughter of a Dutch planter who had been murdered by the Japanese two years earlier. Corrie had been hiding from the enemy for two years before Tarzan came along.
Along the way, they encounter a many groups of Japanese soldiers -- each more nasty than the other -- as well as aband of Dutch outlaws who have been terrorizing the natives, Tarzan fight and kills a tiger, a python, an orangutang, a shark, and Jungle Lord knows what else. Oh...and he also kills what feels like 93 percent of the Japanese on the island. There's a complicated love story between the noble-named Jerry and Corrie*, some treacherous natives, some noble natives, and a whole lot of capturing and escaping. And that's basically the book. (By the end of the novel, Tarzan's group has contained some Americans, some Dutch, a Chinese, and Indonesian, and the British Jungle Lord, thus the "Foreign Legion.")
By this stage in his career, it appears that Burroughs was merely telephoning it in -- at least as far as Tarzan goes. ERB was never a great stylist; his strength was in his fast-paced style and his imagination. His imagination flagged in Tarzan and the Foreign Legion and he satisfied himself with merely moving his players around on a board, encountering and overcoming difficulties as they came. Villains pop up and are quickly eliminated only to have other villains pop up and be eliminated and so on seemingly ad infinitum.
Several sentences in the book make absolutely no sense to such a degree that they could not be printing errors.
Because of when the book was written, Burroughs' jingoism is at full force. There are no Japanese in the novel -- only Japs, who are often referred to as monkeymen and as stupid an unintelligent. Even Tarzan calls the enemy Japs.
Nonetheless, despite the banal plotting and racist imagery, the book moves along quickly and there are enough glimpses of the old Burroughs to make the book readable, although discomforting.
Maybe it would be best for you to skip this one and read some of the earlier Tarzan novels. This one appears to be for completists only.