Shattered Gunline

It happens for the player who claims it, whoever launched it, and at once: claims happen in the battle step, after the crew destroyed there are gone (706.6). Every Mech you control on board when it happens gets one, in your berth or dispatched; there is nothing to choose, and with none, nothing happens (301.7f). Markers stay on a card while it is on board, and several add up; it loses them when it leaves the board (301.7).

Crew dispatched here on their own turn make progress, whoever launched it; on the opponent's turn they can only fight (706.3a). The first player to reach 5 progress claims it and gains 2 spoils.