The answer to your question can be found in Ralph's conversation with Piggy when the two are discussing swimming. While Piggy reveals that he can't swim because of his asthma, Ralph announces that his father taught him to swim when he was five years old and that his father is a commander in the navy. He seems to have absolute confidence that "when [his father] gets leave," he will come and rescue the marooned boys.

Piggy, clearly not wanting to reveal details about his own parents, asks Ralph when this rescue will take place, to which Ralph replies, "soon as he can." His confidence in his father's ability to rescue them cannot be shaken, even when Piggy asks how his father would know the boys' whereabouts.

We get more detail about Ralph's father when his proud son brings him up again in chapter 2. He explains that the navy will find them because, according to his father, "there aren't any unknown islands left." With every island being mapped and labeled in the Queen's "big room full of maps," Ralph shares his absolute confidence that rescue is inevitable. He tells the boys that it may even be his father's ship that arrives to rescue them.

It seems that his father's position helps Ralph to gain the respect of his peers, as the boys begin to clap and Piggy shows his "open admiration" for Ralph. As a good leader, Ralph then points out that in order to help his father, the navy, or other rescuers to find them, they need a fire with smoke on the top of the mountain.

In the first chapter of the novel, Ralph dives into the natural bathing pool and asks Piggy if he is going to jump in. Piggy replies by blaming his asthma and saying he cannot swim well. Ralph responds by saying his father taught him how to swim and mentions that he is a commander in the Navy. Ralph goes on to say his father will eventually rescue them when he "gets leave." It is clear to the reader that Ralph admires his father and has all the confidence in the world that he will find them. At this point in the story, Ralph is an optimistic, naïve boy who has complete faith in his father and the British Navy.

The fact that Ralph's father is a commander also foreshadows Ralph's election as chief. Unfortunately, Ralph does not possess the essential attributes of natural-born leaders and quickly loses control over the group as Jack gains prominence. In the second chapter, Ralph holds an assembly and makes another comment about his father. Ralph reiterates that his father once told him that the Queen has a room full of maps, which will inform the navy of their location. Sooner or later, Ralph's father will arrive to rescue them.

This information gives the boys hope, and Ralph receives a round of applause from the group. Tragically, the boys miss out on their first opportunity for rescue and rapidly descend into savagery before a naval ship eventually arrives.

Like all of the boys in Lord of the Flies, Ralph comes from a very privileged background. He attends a private school, which in Great Britain is an elite institution open only to the sons and daughters of the wealthy.

His father is a commander in the Royal Navy, a position that provides further evidence of Ralph's elite background. Then as now, the senior ranks of the British armed forces were dominated by men who'd been to private school, and so one can reasonably infer that Ralph's father had the same privileged education as his son.

From his brief exchange with Piggy, we can safely infer that Ralph looks up to his father. We can observe this when he expresses the firm belief that, once his father has obtained leave, he will come and rescue him and the other boys on the island. Ralph's overwhelming confidence in his father indicates considerable respect for his abilities.

In the meantime, it would appear that Ralph will be able to take good care of himself, not least because of his remarkable swimming abilities. As he tells Piggy, he's been able to swim since he was five. He was taught by his father—who else?—who clearly wanted to instill into his son some of the survival skills he's learned and has doubtless put to good use in his naval service.

In chapter one there are two places that show what Ralph's father did. In the beginning when Ralph is talking with Piggy, Ralph says that his father, who is a commander in the navy, taught him how to swim. 

Later in the chapter, as Ralph holds the conch shell, he encourages the boys by telling them that help is on the way. He speaks with authority, because his father was a navy man. Moreover, his father told him that there are no unknown islands left. 

Ralph's father works in the navy. On page 13 in my edition we see that Ralph drops this into his conversation with Piggy, perhaps slightly boasting, to answer Piggy's question about how he learnt to swim so well:

"I could swim when I was five. Daddy taught me. He's a commander in the Navy. When he gets leave he'll come and rescue us..."

This perhaps foreshadows Ralph's leadership at the beginning of the novel, and also his role as the representative of civilisation and order in this work. We can also see his youthful optimism at a quick rescue, his dependence on "grown ups" and his inability to see that this experience is not something that they will be rescued from quickly.