At the end of chapter 12 it says "The officer, surrounded by these noises, was moved and a little embarrassed." Why would he be embarrassed?
The final clause amplifies the statement "a little embarrassed." In the final clause the narrator says the officer "waited, allowing his eyes to rest on the trim cruiser in the distance." Both "trim" and "distance" are significant words, suggesting the officer's need to focus on what has order and to separate himself from what does not. In addition, the "trim cruiser" is in the "distance" just as true humanity in the form of goodness is quite far away--certainly the officer doesn't show it. Kind though he attempts to be, he does not want to get involved in the "messy emotions" the boys show.
The officer is embarrassed because Ralph is crying and in the officer's mind and in his culture, proper British school boys do not cry. The officer thinks the boys have simply been playing; he does not realize what has been going on. Golding is showing the reader that things in the world outside of the island haven't changed and the world that Ralph and the other boys will return to will be no better than the one they left. Mankind, according to Golding, is, by nature, savage and the world the boys left was savage because they were at war. The boys on the island became savage and now this officer's response to the boys shows a lack of understanding and therefore, a lack of civility.
My interpretation of the last few pharagraphs of where the officer finally arrives on the island was as if he had stepped into a dream - it was strange that a whole school of boys on an island could be holding their own war. He even jokes about it to Ralph, when he hears narrations of their stay on the island. Even the mobidity of Piggy's death is brought up in a whimsical tone - it is as if the deaths on the island were considered light, insignificant and unconvincing.
His embarrassment probably arises from Ralph bursting into tears and the emergence of some of the boys, running around unclothed with runny noses. Perhaps in his mind, he regrets his lackadaisical attitude towards the boys in the first place. Personally, I think it represents a lack of female instinct displayed by the male gender throughout the book. From the beginning, some of the younger boys found comfort in suckling their thumbs, but the savagery and violence that men generally lean towards, as compared to women, overwhelms the children on the island.
Likewise, the officer displays a lack of concern, sensitivity and even affection towards the boys, who have been through their own little "war."