In order to fulfill this objective, the player must collect various weapons and equipments (including keycards for further access into the fortress), while avoiding visual contact with the enemy. The player must also confront bosses in the form of Outer Heaven's elite mercenary force and rescue hostages hidden within the fortress in order to increase player rank, which gives Snake an extended life bar and increased storage capacity for replenishable items and ammo. The player can use a wireless transceiver to come in touch with their commanding officer, Big Boss, to learn more about their current mission objectives or contact one of the local resistance members operating covertly within the fortress to gain useful tips and insights.