And on board ships, conning officers do not take over "to give the CO a break". There is a regular rotation of usually four hour watches among qualified JOs to conn the ship (CO/XO not among them) as Officer of the Deck (OOD), with special qualifications for underway replenishment, and sea and anchor details. On watch, they have the full authority of the CO behind them. The CO or XO may be on the bridge, but he will only take over the conn during a dire emergency, or if the OOD screws up big time. In which case the CO must announce that he has the deck and the conn, and there must be a log entry made to document the legal shift of responsibility. There is a similar organization in the combat capability, separate from conning the ship. The Tactical Action Officer (TAO) has the weapons release authority, responsibility to fight the ship. In active combat, the CO will normally be in the Combat Direction or Information Center (CDC/CIC) and the XO on the bridge.
If its essential for a JO to take over i'd have all the senior officers either dead or incapacitated - as with the first Ramage book , where he winds up briefly in command of HMS sibella (frigate) (up from third Lt) when everyone above him is killed ... i say briefly because he then blows it up taking a french ship of the line with it, and discharges the secret mission they were sailing on with an open boat ... leading to his promotion to commander and being put in charge of a topsl cutter
In regard of this , in red storm riding Nimitz has just suffered a russian missile strike and the only surviving officers not engaged in fighting the fires are Tolland (the only survivor from the CIC) and the Captain. The Captain gives Tolland the conn whilst he heads aft to deal with damage control... iirc the captain annouces "Mr Bryce has the deck, Mr Tolland has the Conn" ( Clancy really knew his stuff regarding the USN so i'd be surprised if he got this kind of thing wrong)
I intentionally avoided mentioning that movie, as it was hands down the worst Star Trek I have ever seen (given that I loved all the others), with a great emphasis on following your touchy-feely emotions rather than logic, which to me is a recipe for getting yourself and everyone onboard killed. As a counterpoint, I would recommend "Tipping Point" and "Onslaught" by David Poyer, which deals with a very highly automated Ticonderoga--class cruiser, the Savo Island, in very realistic modern wartime scenarios, including a full scale naval war with China. And it deals very well with the agony of command.
I have read Red Storm Rising, and it is a very good book, but I need to go back and check that passage. It is not even legally correct. If the CO is on the bridge, and says, "I have the Conn" , he is temporarily taking over steering responsibility from the OOD, perhaps because he sees a dangerous situation emerging; the OOD is still on watch, and the CO may say later, "Mr x, you may have the conn now," and the OOD will repeat that phrase that he has the conn. Whoever is steering the ship takes orders ONLY from the person who has the conn. If the CO says, "I have the deck and the conn," he has just relieved the OOD, probably for cause. And of course, the oncoming OOD will say the same thing after turnover brief, "I have the deck and the conn." In both cases, the relieved OOD can leave the bridge. I can't see a scenario where the CO (Bryce) has the deck, but is elsewhere fighting fires, and Tolland has the conn, but not the deck.
The CO isnt Bryce - I believe but can't be certain that Bryce is a JO junior to Tolland who is an LT commander .. I think the CO is called Sanchez ( I think that tolland sanchez are the only ones to get out of CIC - certainly the admiral dies, and go to the bridge together where they find Bryce the only surviving officer) IIRC The officers who had both the conn and the deck are dead, killed by blast and shrapnel, so this is a case of exingent circumstances where following the spirit of the protocol is probably more important than the exact letter
