“Chain Reaction” is episode fifteen of season four of Stargate SG-1.
SG-1 are under attack and return to the SGC, but the gate room suffers incoming fire. If General Hammond had closed the iris, as he should have, SG-1 would have died, instead of returning safely. This causes him to consider his position, and to announce his retirement. This means that the SGC will get a new commanding officer.
The new commander reassigns Major Carter to work on naqahdah-enhanced nuclear weapons, and takes Daniel off the front line. He is also less than impressed with O’Neill’s attitude.
O’Neill is convinced there is something more going on, and he’s right, and that Hammond wouldn’t have retired simply because he was fed up. The NID had asked Hammond to co-operate. When he didn’t, his family was threatened, resulting in him deciding to retire in order to protect them. O’Neill has to do a deal with Maybourne. Not his most favourite person.