Who outranks who between a Army officer, Airforce officer, Marine officer, and Navy officer?

Here is how seniority is determined:

1 by rank

2 if both are of equal rank then the person who has held that rank the longest

3) if both were promoted the same day then the person who had been in the military the longest

4) then by age

5) then aplhabetical

6) then somebody either shoots one of them or they flip a coin

Within each service there is a seniority list that makes seniority absolutely unambiguous; in the Navy it's called the lineal list. Between services, if two officers are the same pay grade, then it is determined by date of rank. If they are the same date of rank it is by length of service. If they have the same pay grade, date of rank, and were commissioned the same day, then they would be exactly the same rank.

Interestingly enough, authority to command a vessel in the Navy is tied your status as a line or staff officer. An unrestricted line officer (aviation, surface warfare, submarine service, SEAL) can command a vessel over a a staff officer, i.e. if an Ensign Student Naval Aviator and a Rear Admiral in the Supply Corps are in a small boat, the Ensign has command. He can't issue orders to the Admiral, but when it comes to issues of safe navigation of he vessel, he is the final authority and does not not have to obey orders from the Admiral. Of course, once the boat is docked, if the Supply Corps Rear Admiral tells him to drop and give him 20, he'd have to. But other commenters are correct; unless you are in a specific training environment where it's appropriate like jump school, one officer would never order another officer outside his chain of command to "drop and give me 20."

If for example they were all Captains, the one with the most time in grade outranks the others. Same goes for any officer or enlisted rank. And I don't think you will ever see one officer tell another to drop and give me any. It's that professional courtesy thing.

Depends on the rank of the actual officer.

For instance, an Air force Captain has say over an Army Lieutenant- but not over the standing orders of the Army Major who told him to do whatever he's doing.

Neither. A Four Star General is the EXACT same rank as a Four Star Admiral.

If faced with two people of the exact same rank, then the one who has held that rank longer is the higher ranking.

If they were both promoted on the exact same day, then the tiebreaker is who has been in the longest.

Ted, NO officer will tell another officer to drop down and give them twenty.

Simple, the Military operates under the "O" structure such as:

O1

O2

O3

O4

and so on, so if your an O3 in the Air Force (Captain), then an O3 in the Navy (Lieutenant) is equal to you.

The one with the higher rank wins. If they have the same rank the one with more time in rank and then service wins.

All are equal in rank and all would will tell you the other branches are lower in rank....

A Navy officer outranks the others i believe.