Place one atop Battle Bridge side deck during the seed
phase. Battle Bridge is now open and in play (immune to
cards which close doorways).
OR
Stock in deck and play at
start of ship battle (even during opponent's turn) if you
have Leadership in that battle. Allows you to draw two
extra Tactic cards (cumulative) or enhances each of your
ships' and facilities' WEAPONS +1; then discard doorway.