In Lord of the Flies, chapter 10, who becomes second in command in Jack's camp? Why?

There is no direct or actual nomination of a boy becoming second in command in Chapter 10. But you could argue that Roger takes up this position by default. In other words, Roger assumes this position by himself. When he approaches the Castle Rock, he is not surprised to be greeted and confronted by a guard, Robert. Roger tells him that he could not stop him if he was determined to pass. But Robert shows...

There is no direct or actual nomination of a boy becoming second in command in Chapter 10. But you could argue that Roger takes up this position by default. In other words, Roger assumes this position by himself. When he approaches the Castle Rock, he is not surprised to be greeted and confronted by a guard, Robert. Roger tells him that he could not stop him if he was determined to pass. But Robert shows him a rock poised to fall on anyone who he would want to deter from entering. Roger admires this use of the threat of violence. 

Robert also informs Roger that Jack plans to beat Wilfred. The reason is unknown. Roger has something of an epiphany here. This appeals to Roger because he has, or has chosen to have, a penchant for violence and intimidation. The fact that the tribe is now beating dissidents gives Roger a greater sense of purpose; this shows an opportunity for more violence in the future. It seems that Roger might consider himself the most likely enforcer of such violence. And from this epiphany, Roger foresees that he will assume this authority, albeit with Jack remaining as chief. Roger assimilates "the possibilities of irresponsible authority." In other words, Roger understands the possibility that he will be able to utilize his desire for violence. He will be able to utilize this irresponsible authority.