In chapter ten, Ralph, Piggy, and Samneric try their best to maintain a small fire and begin to lament their unfortunate situation. At this point in the story, the majority of the boys have joined Jack's tribe of savages at the other end of the island, and they have all participated in Simon's brutal murder. For Ralph, Piggy, and Samneric, their spirits are at an all-time low and they recognize that things will never be the same. While they attempt to keep the small fire lit, Ralph reveals his cynicism by saying,
We might get taken prisoner by the Reds. (Golding, 233)
Ralph's reference to "the Reds" is an allusion to the Soviet communists, who formed the Red Army. Lord of the Flies was published in 1954, which was nine years after WWII ended and during the time when the United States was involved in the Cold War with the Soviet Union. During the Cold War, Britain was allied with the United States, which explains why Ralph views the Reds as enemies and fears becoming their captive.
Ralph recognizes that there is a possibility that the Soviet communists will find them on the uninhabited island before the British and they will become prisoners of war. Eric responds to Ralph's comment by saying that being captured by the Reds would be better than being taken prisoner by Jack and his band of savages. The fact that the boys would rather be captured by the Reds than Jack emphasizes his brutality.
The "Reds" are the Soviet communists who controlled Russia at that time. Red is a color associated with both communism in general and the Soviet Union, as it was the color of the Soviet flag.
The few boys—Ralph, Piggy, Sam, and Eric—who have not joined Jack's group or been killed are trying to get the fire going despite the rain and damp. They need a big fire with lots of smoke if they are to have any chance of attracting a passing ship or plane. They also need the fire for comfort and warmth at night.
When Ralph makes the comment about the Reds, he is showing signs of hopelessness: the implication is, what difference if we have smoke or not, because we might just as well get captured by the enemy communists. However, as Eric points out, even that would be better than falling into the hands of Jack's murderous, barbarous group.
Despite all their efforts, the four boys have to give up on the fire for the night. This is a low point in the novel. The fire is the symbol of civilization. The four remaining civilized boys's inability to keep it going indicates that they are falling away from civilization, reverting back to a more primal state.
In Chapter 10, there is a deep division between Jack and Ralph, and tensions are building to a climax. They have already taken part, either directly or indirectly, in Simon's murder, and Piggy and Ralph especially are feeling unsettled by the apparent declining morals of the entire group. As they talk, Ralph notes, "We might get taken prisoner by the Reds." The use of a proper noun here directs us to history.
After the Bolshevik Revolution of 1917, the Soviet Communist government created the Red Army. Therefore, Ralph is noting the tensions that exist in his world where Britain has entered a war against Communist Russia. Ralph is afraid that if they are found and rescued, it will be by the enemy of their own country.
Eric notes that even this would "be better than—" but never finishes his thought. The implication is that being a prisoner of the Communists would be better than continuing to live with Jack or possibly with the dead man in the parachute who haunts them.
By "the Reds," Ralph means the Communists, or the Soviet Block.
Golding wrote "Lord of the Flies" in 1954, nine years after the end of World War II, in which he served. It was the time of the cold war. The threat of nuclear conflict between the Soviets and the West was very real (at least in people's minds), and Golding implies that World War III, were it to happen, would result from the hostility between the forces of democracy and communism.
In subsequent comments, Golding has suggested that the novel may be considered a fable about the weakness of democratic societies (Ralph's lot) in the face of powerful dictatorships, such as those of Hitler and Stalin (or Jack). The allusion to "reds" brings us back to that level of interpretation, giving us another, political, level of understanding of the book.
Actually, Ralph is referring to whomever the British are fighting during this time. Remember that the novel is set in the future during an atomic war. We, as an audience, are not given an actual enemy for England, but it's severe enough to warrent evacuation. In chapter 10, Ralph, Piggy, and Samneric are discusses the things they would like to have on the island now. The suggestion of a boat comes up...:
"Ralph dredged in his fading knowledge of the world.
'We might get taken prisoner by the Reds.'
Eric pushed back his hair.
'They'd be better than-'"
The boys are actually comparing what Jack and his tribe have done and are doing to what some foreign country has done to England during this future war. They are deciding who it would be worse to be captured by.