Moving beyond the basic “the most senior officer is in charge” during an emergency, I have some questions on how far that extends. So for the sake of argument assume an emergency and shit has to be dealt with RFN. If there is a difference between it happening in a warzone or not let me know. Would these people be in command and be responsible for issuing orders if they held the highest rank around?
Most senior office is not a line office but a staff officer. Like if the senior officer is a Major in the JAG office.
A foreign officer but working as a member of the officer corps. I’m thinking Lionel Mandrake in Dr. Strangelove.
The most senior officer is walking by at the time but is not in those soldiers direct chain of command.
An officer in another branch of the service, like a Navy Captain on an Air Force base.
Any officer above a certain rank, like a general is always the senior officer no matter what (unless a higher ranking general is around).
In general, the most senior line officer in the chain of command takes charge, especially if the goal is to continue doing whatever the unit’s original mission is.
Someone outside of the chain of command had better have a pretty compelling reason to take charge if they want anybody to follow them.
A flag officer or general is much more likely to give orders to the unit commander (if appropriate), not try to personally take charge of an individual unit. Like if a flag officer is onboard a ship, and the ship commanding officer is incapacitated, the flag officer does not take command…they instead continue their normal flag officer duties, and next person in the chain of command under the CO takes command of the ship.
The answer to all of your questions is, “It depends”.
In general, the officer with the highest rank in the chain of command of a military unit is in charge of that unit and can give direct orders to any member (but for the purpose of unity of command are generally passed down through the appropriate chain). If that chain of command is completely broken (i.e. there are no officers in the chain of command available), the hierarchy of command goes in terms of service, top level and subordinate command structure, and then rank. So, in general, an Air Force officer can’t give commands to a Army officer of lower rank or even an enlisted; officers within a service but in a different command structure don’t generally give orders outside of their command hierarchy, and as a rule nobody is obligated to take orders from an officer from a foreign service. There are specific exceptions to to all of your conditions, especially if the command hierarchy is out of communication or completely broken, or a soldier/sailor/airman/marine has been seconded to another unit or foreign service.
There is a Tom Clancy novel (Red Storm Rising, I believe), where a US Air Force lieutenant (who is a meteorologist) ends up in command of a UK Special Air Service unit because their officer was killed while parachuting. It is basically the most ridiculous thing in that novel, both that a USAF officer would have command authority over a British unit, and that SAS troops would take orders from a weather nerd. But it was necessary so the author could put them in a completely contrived situation in what was otherwise a pretty decent prognostication of a European land war.
That’s why I specified an emergency situation. Would that be a case of chain be damned and whoever has the highest rank is in charge?
What if there were a situation like D-Day with a coordinated attack with different nations. An American squad has been cut off and officers killed. All of the sudden a Canadian captain shows up. Would that be an exception?
To expand upon this, the reason for this is because the flag officer has a specific role (to oversee the order of battle) and may not be knowledgeable about the operations or personal competencies of a particular unit (unit being any command structure; a platoon, a ship, a squadron, whatever). So the next senior officer within the unit takes charge–even if it is an NCO–and the flag officer keeps doing their job so as not to interrupt the effective leadership of the unit.
An NCO would take over the squad (and is probably the one giving the real direction, anyway, while handholding his lieutenant and trying to keep him from getting killed). The NCO make take ‘suggestions’ from the Canadian officer in such a situation for tactical reasons of coordinating tactical efforts, but the sergeant isn’t required to take orders unless there is some specific interservice direction.
There are specific situations where a warfighter might be attached to a group of another service, like an Air Force TACP or Pararescueman attached to a Ranger RRD or an ISA unit, in which they will take orders from a more senior officer or NCO of another service. This has become especially common with joint service operations and especially within the Joint Special Operations Command (JSOC). But as a general rule, officers of one branch, or within a branch but in a different command structure do not give orders outside of their hierarchy or even to significantly more junior officers or enlisted unless they are specifically on that officer’s staff.
Like @Stranger_On_A_Train said, it depends entirely on what the emergency situation is. There are too many variables to give a coherent answer.
The best answer is “maybe,” but probably not. The Canadian officer would likely not be familiar with American tactics, training, or terminology. If anything the Canadian officer might strongly suggest that the senior noncommissioned officer (NCO) take a certain action, but the NCO would likely not be obligated to follow these orders.
ETA: I see that @Stranger_On_A_Train and I have given nearly identical word-for-word answers to the hypothetical D-Day question.
I’ll just add to what @Stranger_On_A_Train and @robby have said on the matter "and the American NCO would almost certainly follow the Canadian officer’s ‘suggestions’ until such time as things had sorted themselves out. Joint US/Commonwealth operations were very common during WWII, for the D-Day landings themselves the command structure went Supreme Commander, Allied Expeditionary Force -Eisenhower (US) → Allied Ground Forces Commander (21st Army Group) Mongomery (UK) and only under that split into American landing sector ->1st US Army (Bradley) and British/Canadian landing sector → 2nd British Army (Dempsey).
An even more extreme example was the Anzio landings, which were under the operational command of US VI Corps, which was commanding the 1st British Infantry Division and 2nd British Commando Brigade as well as the joint US-Canadian 1st Special Service Force along with the US 3rd and 45th Infantry Divisions and what was known at the time simply as the US Ranger Force.
Map of the situation after the initial landings:
As forces continued to be sent into the Anzio beachhead, US VI Corps was at its height commanding 1st, 3rd and 56th British Infantry Divisions as well as 3rd and 45th US Infantry Divisions and the 1st US Armored Division.
Would “specific interservice direction” be something like NATO? I mean, I could see that if you had a dozen Royal Marines with a Lieutenant, a half dozen US Marines, 3 Danish NCOs, a German Captain, and an Argentinian Colonel in some sort of emergent situation, that the NATO troops would self-organize under the German and British officers, and the Argentinian guy could help out or not.
