Marines rally as they fall back.
The HQ Characters' entry states that they are Independent Characters unless accompanied by a Bodyguard. The Armory section then goes on to list items, and note that many can only be taken by an Independent Character. Terminator-only items and can still take items that Terminators cannot take, like grenades. The Marine player may wait until his whole squad has fired to see which die he re-rolls but may not progress any hits to wounds or wait to see how the other player allocates the hits before deciding. It is only a defensive item.