Q-ships are not declared as such when deployed onto the table; the owning player must write down which freighters are Q-ships at the start of the game. The owning player may reveal the ship as a Q-ship at any time during the game; it is, obviously, also revealed as a Q-ship if it is hit twice by enemy fire (thus producing two blast markers.) It is permissible for the owning player to ‘hold back’ one of his Turrets if the Q-ship is attacked by enemy attack craft (to avoid revealing it), but this is a dangerous gamble.
Q-ships do not count as freighters for victory conditions, as they have no transport capacity.