The officer grins and asks, "What have you been doing? Having a war or something?" What are the two ironies here?Chapter 10

 E-notes defines irony as "a dryly humorous or lightly sarcastic figure of speech in which the literal meaning of a word or statement is the opposite of that intended. In literature, it is the technique of indicating an intention or attitude opposed to what is actually stated."

First of all, it is ironic that the Officer who is fighting in an adult war would question whether the children are at war. Secondly, the boys have been at war, and Ralph has nearly been killed and, of course, both Simon and Piggy have been killed! It is also ironic that the Officer says the boys are all "British boys," and implies as such, they would have good manners, and be raised without the ability to revert to the savagery that war demands, yet we know the boys have easily reverted to savagery and, at the same time, the British adults are engaged in war!