!!'''Captain Marcus Chaplin'''
->Played by: Andre Braugher

The commander of the USS Colorado -- an experienced and well-respected submariner who one day gets a suspicious order to launch nuclear missiles at Pakistan.

* BaldBlackLeaderGuy
* TheCaptain
* AFatherToHisMen: was willing to surrender to government authorities in exchange for amnesty for his crew--and in fact was on the verge of signing the deal when it was literally pulled from the table in a double-cross.
* GuileHero
* [[spoiler: TheHeroDies]]
* [[spoiler: HeroicSacrifice]]
* ObfuscatingInsanity: How he hopes to prevent anyone from attacking the island. At least, we hope he is faking it.
* ScaryBlackMan: Played with--if you have exclusive control of an SSBN with 17 Trident missiles on board, and are [[ObfuscatingInsanity not acting like you're in your right mind]], you're pretty scary no matter what race you are.
* ScrewTheRulesImDoingWhatsRight: PlayedWith, in that Chaplin ''was'' following the rules in questioning an illegal order from an unauthorized source, even if it meant going against his chain of command.

!!'''Commander Sam Kendal'''
->Played by: Scott Speedman

The Colorado's XO. He's willing to follow Chaplin into apparent treason, but the way the government has been treating his wife Christine back home has been shaking his loyalty.

* HappilyMarried: By all appearances.
* TheLancer
* MarriedToTheJob: According to his wife, she is his "other woman"; he's married to his country.
* NumberTwo

!!'''Lieutenant Grace Shepard'''
->Played by: Daisy Betts
The daughter of Admiral Arthur Shepard, and to all intents and purposes the third in command of the Colorado. She has trouble gaining the respect of the enlisted crew, especially COB Prosser, until [[spoiler:commanding the sub on a repair mission, staring down three US attack subs and pulling off a nearly impossible rescue in the process]].

* ActionGirl
* DudeWheresMyRespect: She's the third-ranking officer and highly capable under pressure, but she's also a young woman, and quite a few people assume she's there because of {{Nepotism}}.
* FirstNameBasis: In a negative way. Prosser tends to address her by her first name instead of her rank or last name as a sign of disrespect.
* TheNeidermeyer: PlayedWith, in that she does eventually gain the respect of the crew and the COB by showing just what she is capable of under pressure.
* [[spoiler: RapeAsBackstory]]
* [[WellDoneSonGuy Well Done Daughter Gal]]: Subtle but present; she feels she has a lot to live up to.

!!'''Master Chief Joe Prosser'''
->Played by: Robert Patrick.

The Chief of Boat (senior enlisted man on the sub), and a close friend of Chaplin until the launch order comes in, at which point he turns on Chaplin and threatens to personally turn him in for treason. Nevertheless, Chaplin can trust him for the time being, because, as Prosser says, if he left, he'd be missing a front row seat for the end of the world.

* BerserkButton: Don't try to peddle drugs to any US Navy personnel or you're in trouble.
* JerkWithAHeartOfGold: Emphasis ''strongly'' on "jerk," but he has his moments.
* MyCountryRightOrWrong
* FatherNeptune / SergeantRock: Prosser has the loyalty of most of the crew and is clearly the 'old salt' on the boat. Chaplin ultimately has to admit that he can't manage the crew without him.

!!'''SEAL Officer James King'''
->Played by: Daniel Lissing

The acting commander of the SEAL group picked up in the pilot, and by his own belief the one most directly responsible for the entire fiasco. He has no loyalty to Chaplin or the Colorado, but he's along for the ride, and proves very effective when his services are needed.

* AntiHero
* {{Badass}}
* ChildSoldiers: King admits to Sam in Manila that he signed up for the military at 17 with fake documents to get away from his family life.
* DatingWhatDaddyHates: He was the go-to guy for pissing off girls' dads back in high school.
* DrowningMySorrows: Almost the first thing he does on the island is find a bar and start a tab.
* IChooseToStay: In the finale, he decides to remain in the island and begins a relationship with Tani.
* MyGodWhatHaveIDone: In the pilot.
* SuperNotDrowningSkills

!!'''Petty Officer First Class Pilar Cortez'''
-->Played By: Jessica Camacho

A female officer on the sub, who was kidnapped with two other sailors by Serrat, with whom she attempted to make a deal to keep all three of them alive, which didn't work. [[spoiler: Recently revealed to be the CIA mole]]
* ActionGirl
* TheDeterminator
* [[spoiler: TheMole]]
* SpicyLatina

!!'''Kylie Sinclair'''
->Played by: Autumn Reeser

A young, attractive woman who happens to be the daughter of the owner of a major defense contractor, who's involved in the story because of the Perseus Project, a degaussing device meant to mask a submarine's magnetic field underwater. Though at first glance she seems to be a bit of a promiscuous party girl, she's also very intelligent, manipulative, and determined to both protect her company's project and get to the bottom of the developing scandal in Washington.

* AmbiguouslyEvil: She's all to happy to use her knowledge of the US Navy blowing up a hundred and fifty Americans on its own submarine to blackmail them into putting her prototype put on more subs, but when it turns out to be something darker, she won't let them sweep it under the rug.
* BlondeRepublicanSexKitten: She's a brunette, but aside from that she is basically the face of the military-industrial complex, and describes herself as "politically straddling a line just to the left of Attila the Hun"
* BrainyBrunette
* RichBitch: She's aware of it, though, and says she's working on it.
* SpoiledSweet, although just barely; she's shown to have a rather bratty public persona, but a strong sense of justice behind closed doors.

!!'''Christine Kendal'''
->Played by: Jessy Schram

Kendal's loyal wife, currently fending off governmental gaslighting attempts to break her loyalty, as well as trying to make as much of a scene as possible in front of the press to encourage investigation into the whole mess.

* CassandraTruth: She knows that her husband (and by extension the ''Colorado'' and its crew) is being set up but doesn't help her cause by going ballistic on the media vans parked outside her house--resulting in Christine being painted as a nutjob by the media when footage of her tirade goes viral. The trope may be defied later on now that Christine is talking to the media in a more cooperative fashion (and has gained Kylie Sinclair as an ally on the inside).
* DangerouslyGenreSavvy: Makes her husband's old friend as a government agent trying to break her within two days.
* HairOfGoldHeartOfGold: Despite everything the government throws at her, she never wavers in her belief in Sam.
* ObfuscatingStupidity: It would be easy, especially in the first couple of episodes to think that she's a DumbBlonde. She isn't.

!!'''Tani Tumrenjak'''
->Played by: Dichen Lachman

Introduced as a bar owner on Sainte Marina in the pilot, Tumrenjak is the daughter of an island native who raised her in Australia, then returned. She became involved with a despondent King when he came into her bar to drink himself blind after Chaplin's mutiny.

* TheBartender: The bar owner, actually, but it's a small bar, so she serves drinks and cleans up.
* FakeNationality: As pointed out on the main page, Dichen Lachman is ethnically Tibetan, born in Nepal, and raised in Australia. Come to think of it, Tani doesn't look much like her island native family either.

!!'''Julian Serrat'''
->Played by: Sahr Ngaujah

The real power on the island, at least until the Colorado shows up, Serrat is a ruthless drug lord who doesn't deal well with the loss of standing when an American sub captain sails one of the deadliest ships in the world into his harbor.

* DamnItFeelsGoodToBeAGangster: Serrat is undisputedly the top dog on the island until the ''Colorado'' shows up (and even Chaplin has to work around him for the time being).
* FakeNationality: Ngaujah is American, with family from Sierra Leone; Serrat is said to be from Liberia. [[note]]Interestingly, Sierra Leone and Liberia both have similar national origins as havens for freed slaves; Liberia was founded by Americans, while Sierra Leone was founded by British subjects, mostly from the Caribbean. But that's more an interesting coincidence than anything else.[[/note]]
* JerkAss
* JokerImmunity: No matter what he does the show comes up with excuse after excuse for Chaplin not to simply kill him.
* ManipulativeBastard: In one episode, he agreed to declare the accused rapist not guilty, knowing the islanders would riot in anger.
* ScaryBlackMan: at least until he meets up with Chaplin, who's an even ''scarier'' black man.
* VillainousCrush: On Sophie.

!!'''Sophie Girard'''
->Played by: Camille de Pazzis

A French civilian NATO employee who helps operate a listening post on Sainte Marina. Her cooperation with the Colorado's crew seems reluctant (especially as she watched the nuking of Pakistan in real time on satellite monitors, nearly having a breakdown in the process), but she's clearly smitten with the very married Kendall.
* AllLoveIsUnrequited: Her love with Kendall. [[spoiler:It leads to her kissing Kendall when he is drugged.]]
* BrainyBrunette