Bridge officer
A bridge officer was an officer whose station or main duties took place on the bridge of a starship. For a bridge officer to be eligible to take command, the Bridge Officer's Test had to be passed.
If a non-bridge officer and a bridge officer held the same rank, the bridge officer was considered the ranking officer.
Orders on the bridge
There is a definitive but fine line in the Chain of Command on the bridge and often times that line gets blurred in the midst of a crisis. Different situations call for different command structures, although the Captain is always the final word on any given order.
Relieving the standing Bridge Officer
When an officer is placed in command of the bridge by either the Fleet Admiral, the Captain, the XO or the 2nd Officer they retain that command unless they relinquish it to a higher rank or are relieved by either the 2nd Officer, the XO, the Captain or the Fleet Admiral. If an officer is placed in command, a higher ranking officer that is not a part of the command staff cannot relieve that officer, no matter what the standing bridge officer's rank or position. It is customary for the junior officer to offer command to the ranking officer and it is customary that unless there is a pressing need the senior officer will decline the offer and let the junior officer continue their watch.
Priority of officers
Bridge officers have priority over non-bridge officers to have the bridge, unless there's an emergency situation. In the situation where a higher ranking officer is on the bridge who isn't a bridge officer and lower ranking bridge officers are present, the highest ranking bridge officer has the bridge, unless another officer is placed in command (see above).
In case of an emergency situation which qualifies as a red alert the highest ranking officer of the ship's chain of command present on the bridge has the bridge.