When is a Navy Captain referred to as 'Commodore'? When is a Lieutenant called 'Captain'?

A Navy Captain is a Commodore when he is in command of a squadron of ships, such as DESRON 15
In 24 years I never heard of a 0-3 Captain called anything but Captain because that's what he is, I am not a military expert and I suppose that there could possibly be some situation where it would occur I just can't fathom where that might be.
A Lieutenant is referred to Captain when he is in command of a ship and that can apply to LCDR and CDR as well when they are CO of a ship.
Boats is a Boatswain Mate regardless of rank.

Commodore was used for a specific pay grade for a short period of time and not just a positional title. What pay grade was this?

1. Time of war as a fleet commander.

2. No clue

3. When in command of a sea-going vessel.

Bonus guess: Boatswain

Commodores are in charge of squadrons, normally, it's a position, not a rank.

Captains are never referred to as "Major", at least not Navy Captains. I found something on Google that indicated Army and Marine Corps Captains may be referred to as "Major" to avoid confusion on a Naval Vessel. Never heard that one before.

Anyone in command of a vessel is referred to as Captain, regardless of rank.

Boats is any rated Boatswain's Mate.

I think Commodores wear a single star, so when the Captain wears a star. Used to be a wartime only rank but lately have seen Commodores on carriers when I watch videos. All skippers are called Captain regardless of rank, otherwise below CDR addressed as Mister. Boats is a BM Rate.

That's actually pretty good...there were a cpl of others I'd known of, as naval idiosyncrasies, obv good ones, of course just stuff I'd heard or picked up, as well as read about, at various times. There was something about approaching a senior officer, I'd always heard one is to say, "By your leave, sir/ma'am", though I don't know how modern sensibilities mightndictate use of rank, rather than themsir/ma'am, now, I'd read about that trend of late also, of course. Next, I'd read that, espec as late as ww2, e.g., the senior flag rank commanding a shore based naval installation was typ made commodore. I'd read of e.g., on the Wikipedia page for radm grace hopper, that I'd sent in a cpl of wks back, some on here actually knew and or had met her, the famous comp sci expert, that she'd actually been made commodore before radm lower half. That's another naval idiosyncrasy, the whole lower and upper half thing, and the whole jjunior grade or j.g. thing, as well, though I'd seen many countries differentiate between Jr and SR company grade ofcrs in similar fashions, not just j.g. or the whole 2nd/1st Lt thing. Then there's the whole UK pronunciation of lieutenant as " leftanent", another country based idiosyncrasy, as well. I knew of the spwhole shore naval installation thing during ww2 for commodore, or, I'd also read, head of a naval task force, at least some time back, I recall, as, in the book In Harms's Way, about the whole USS Indianapolis tragedy, one of the shore installation commanders involved in the search for them ship had been mentioned as being a commodore. Then, also, there's the whole naval thing of "frocking", the analogue to "pinning on" higher rank in army and USAF, I'm not sure how USMC does it, I'd expect USCG, NOAA corps, and usphs corps, also do frocking, as well as US maritime SVC or USMS, being sea svcs, as well. I also know there's that whole thing of waiting for Senate approval before pinning on, the CO of my unit, whom I'd mentioned speaking with once for an hour an experience in itself, I can tell all of you, was a Col waiting to pin on though apprvd for BGen. The usage of Maj for multiple Capt on board a vessel, I hadn't heard or didn't recall, that's interesting, of course. The whole Boats thing apfor a Bosun I'd heard, at least in a merchant marine context, though ocsnly from a naval or sea SVC perspective. There's also the whole CWO usage of Chief, and the whole usage of senior enlisted total ranks as a mode of address, e.g., master chief in Navy or USCG, or, I'd seen in USAF, referring to a CMSgt as Chief on occasion, ever since USAF eliminated warrants. When I was army ROTC before going USAF OTS, the ROTC unit I was in had a CSM I'd heard and addressed fully as command sergeant major, per se, and also a master sergeant addressed as such, as well. Those were just some other aspects I'd noticed I'd figured worth including here, I'd be eager for any thoughts, good topic, honest, interesting minutiae, many thanks, hope was of interest.

I've never quite understood, admittedly, the whole thing about commodore vs rear admiral lower half. I'm aware that shore installations, especially major port facilities during WW2, especially in the Pacific from an account I'd read of the USS Indianapolis called In Harm's Way, great book, mentioned that, also in the film version of the story with Stacy Keach, good film rendition, refer, I believe , to there having been a commodore commanding a shore installation involved in the search for the ship. The only thing that always strikes me as more than slightly crazy about the whole thing is the seemingly continual back and forth about the usage of the title, that's all. I understand that many naval traditions while worth being kept by all means have purpose and meaning, I just never entirely understood entirely the need for having rear adm upr and lwr halves, when the commodore title was available for use terminologically, that's all I'm trying to convey, I'd be most eager for any thoughts, many thanks just historical curiosity, honest. It's rather like the whole thing about ADM Dewey being ADM of the Navy, the whole thing with gen Pershing as genl of the armies actually on his tombstone I've seen the picture, and genl Pershing having opted for four gold stars for his uniform, instead of the normal four silver ones, in place of a six star circlet five like those of gens Eisenhower or the other five stars , with one in the center, which always just struck me as the completely logical approach, you know? Granted such senior officers have option to choose, or it depends on how Congress approves things, I realize that, it's just that such erratic arcamia, if you will, while of historical interest, certainly, is seemingly calculated as deliberately designed to drive the serious student of history to distraction lol. I've also never understood why, e.g., the chair and vice chair of the jcs since therell obv eventually quite deservedly be females in those roles, OTS obv inevitable to me only a matter of time, aren't given five or six star rank, akin to the whole field marshal and or grand admiral European traditions. I realize ww2 was a unique case, and that there'd been a comgrsnl effort to promote genl MacArthur to six stars which I'd read Jed aprntly said to pls stop, I'd gathered, I just figured I'd mention all those thoughts here, for whatever debate such ideas on my part might engender, many thanks.

A commodore is a captain who has the responsibilities of an admiral. Commodore used to be an actual rank prior to the creation of rear admiral lower and upper halls. This was dropped because Commodores were seen as being part of the admiralty so the rank was renamed rear admiral lower half to avoid confusion with the previously existing rank of rear admiral. Commodore is now more a title of responsibility rather than pay grade.

An O-3 is referred to as Captain when he or she holds the position of commanding officer. I worked for a Captain that was a Commodore. He had Command of a Squadron on ships. I believe this is why they are called Commodore.

1. When he commands a TF or group.
2. When he is the Commanding Officer of a shipboard Marine detachment.
3. When they command a vessel.
4. Boatswain Mate, the senior rate in the Navy.

Boats would be the E6 aka BM1 usually in Ops.

1) Another reason for a Captain to be referred to as "Commodore" is if he's riding a ship that he doesn't command - a ship only has one Captain.
2) No idea - I'm retired Navy, didn't pay too much attention to the minutia of other services.
3) When they are the commanding (officer / authority) of their own craft.

Bonus - "Boats" is the name that a competent Boatswain's Mate is referred to by members of his crew. The "Boatswain" is the senior Boatswain's Mate (usually is either a Warrant or LDO) on a ship.

V/R
"Boats"

I don't know why I didn't think of this before. A nickname for Marine captains is 'skipper'. This just helps avoid Navy officer insecurity.

(Totally kidding. Honest.)

Walt

You got me on most of these questions ! As for Commodore I was Attached troop with Beach Masters on board the USS La Salle & the flag ship of our Group. The Commodore was a full Captain this was the first time I even knew there was such a rank ! Would he be filling an Admirals position & the reason to be called commodore? As to Lieutenant Army, Marine & Air Force would call him Captain. Senior Chief - Master Chief ? Must be some kind of training, NO idea !
Looking these up for answers on internet...

1. When the O-6 CAPT has more than one command or ship under his/her command.
2. Usually when they make the rank of Major. Could also mean that O-3 is a MAJOR _______.
3. When they assume command of a ship.
4. Slang for Boatswain Mate. This can be a good thing or a bad thing based on whether that person chose that rate or was forced on them by flunking out of "A" school.

Got anything harder? Here is one, why is a ship referred to as she or her?