It is 1941 in German-occupied Belgium.
Nazi officers invade a small town and hang four unidentified men in the town square near
the church.
The Commandant arrives with additional soldiers to survey the execution’s aftermath.
Suddenly, two men from the Flemish resistance fire a rocket launcher from a building to
disrupt the proceedings.
Surprisingly, the four hanged men awaken, revealing their ruse as they draw guns and
shoot the entire platoon except for the Commandant.
Their leader Stan walks up to the Nazi official and punches him as he surrenders.
In London, Captain Maes of the Belgian Army convenes with British officials to discuss
a secret mission that will put the Allied Forces ahead of the Nazis.
The Flemish resistance fighters are chosen, but they argue whether they are fit for the
task due to their unorthodox methods of infiltration that earned their infamy in the British Government.
Captain Maes keeps mum about their whereabouts but promises they are the best group to undertake
the insane plan considering they are facing desperate times.
Meanwhile, the resistance fighters return to their camp and torture the Commandant by
drowning him in water during the interrogation.
One of the fighters, Werner, operates the radio to inform the officer on the other line
about securing the 'package.'
Though a recovery team will be on their way to pick up the Commandant, Stan loses his
patience and throws a grenade on the tub that kills and beheads the Nazi officer.
Elsewhere, Captain Maes visits German U-Boat Commander Franz Yeager in prison to offer
him a deal in exchange for an early release.
Franz is devastated to discover his eldest son drafted for the war, was killed in action.
Though initially hesitant to switch sides, the Captain shows a picture of his youngest
son, reminding him there is still a chance to save him.
Later in the camp, female resistance fighter Nadine and her boyfriend, Filip, practice
aiming with a powerful B cartridge that explodes on impact, as demonstrated on a nearby tree.
While the rest of the men enjoy the afternoon with merriment, Stan is in the middle of a
restless sleep, plagued with nightmares of his past.
In the dream, the Nazi officers force him to watch as they kill his wife and leave her
ring in his pocket.
The Gestapo Commander, Kirchbaum, continues questioning him about the location of the
Jews he helped hide.
Still, he remains silent and spits in his face.
Angered, the Commander tries to drown him in the bathtub.
Stan suddenly awakens from his troubled sleep as his daughter, Nadine, tends to his wounded
wrist.
Shortly after, a Belgian messenger arrives to recover the briefcase of the German Commandant.
Still, he is disappointed to find the officer dead.
He gives Stan an envelope containing information about a crucial mission in the Belgian Congo.
The leader lingers with the dossier, considering the group has had more success operating in
their homeland.
Still, the messenger convinces him to accept as their success will result in many German
casualties.
Some days later, the group rendezvous with Captain Maes as they board a German U-boat.
During the debriefing, they learn that their objective is to transport a cargo of Uranium-235,
purchased by the U.S. Government, to New York City.
Once there, the shipment will be used to build a powerful nuclear weapon to level a city.
Shortly after, Franz arrives, but Stan tells the Captain he is unwilling to collaborate
with a German, despite the expertise he can bring.
Nonetheless, Franz immediately discusses the fundamentals of handling the U-Boat, including
a tour of the facilities, allowing the crew only three weeks to learn.
Though the vessel can launch torpedoes, the Captain prohibits using weapons to stay as
a transport ship.
The unit later gets assignments on where to station on the U-Boat, except for Nadine,
who Stan insists on leaving behind on a plantation in Africa since he is protective of her.
Over time, the men become proficient in handling the submarine through the instructions of
Franz and Captain Maes.
One night, after a brisk swim, Nadine spends one more romantic evening with Filip, telling
him Stan cannot be convinced to let her stay in the boat.
A new day arrives as a few burly African workers load the cargo into the submarine.
Suddenly, Werner intercepts a German radio transmission.
Filip spots German warships headed their way, forcing the crew to set out for America earlier
than expected.
Captain Maes argues with Franz, but the German hesitates to accompany them as it is separate
from the deal.
Minutes later, the men discover the Captain dead after being stabbed by Franz.
Stan is about to kill him but is stopped by Filip, knowing they will need him to operate
the boat.
Nadine rejoins the group, along with a French-speaking Congolese worker, Jenga, left behind by his
traitorous employer.
They leave the port promptly, successfully evading capture by diving into the sea.
Stan, now in charge, temporarily handcuffs Franz to ensure he will not betray them.
Problems arise as the toilet floods and chlorine gas leaks, forcing the crew to rise to the
surface.
Unfortunately, they spot a German plane circling above, but while they attempt another dive,
Stan promptly shoots it down with a flak gun before it targets them.
The submarine arises, saving him from drowning.
Later at night, Stan relives the horrors of the night his family was killed.
Kirchbaum holds his newborn baby, threatening to kill him.
He relents, revealing the Jews hiding upstairs behind the fireplace.
After eliminating them, the Commander leaves the baby sitting on top of the tub, but he
falls off balance and drowns, with Stan unable to unchain his wrists to save him.
He awakens from his nightmare and stares angrily at Franz as he sleeps.
Sometime later, Franz notices the ship is off course by 50 degrees, prompting him to
investigate the cause.
He goes to the engine room and discovers Filip ignoring his duties by sleeping with Nadine
behind the machinery.
Stan arrives and checks in with Franz, only to become enraged, catching Filip half-naked
under the blanket with his daughter.
He orders the men to open the missile hatch, preparing to launch him out of the submarine.
Fortunately, Nadine stops him, demanding to be given an everyday life to love someone.
Learning that Stan will only relent when she ties the knot, she asks Franz to marry her
and Filip immediately above the submarine.
Though not legally granted authority to officiate the ceremony, he happily agrees, only to cut
the wedding short when another German U-Boat forces them to dive underwater.
Shortly after, the unwed pair discuss their future.
Nadine airs out resentment for her father, wishing to be with her mother instead after
they get married.
Unfortunately, Filip tearfully reveals that her mother and younger brother were killed
by the Nazis, a moment he witnessed as he rescued Stan from his bondage during that
horrific night.
He apologizes on behalf of her father for not telling her sooner.
Suddenly, Werner loudly alerts the crew that a torpedo is fast approaching.
Everyone gets to their battle stations as Franz orders the submarine to dive deeper.
Fortunately, the torpedo barely misses the top of the vessel.
The crew stops the engines and stays quiet as a German submarine surveys the area for
anomalies.
Franz orders Klisse and Van Pragg to manipulate the circuitry of one of their torpedoes, ensuring
only the fourth and fifth wires are cut.
Minutes later, Werner continues checking on the radio channels of the enemy vessel when
he accidentally tugs on the switch of his record player, turning it on.
The music gets loud enough to be heard outside, forcing the crew to restart the engines and
retreat, knowing they have been discovered.
Eventually, the duo completes their objective and prepares to lift the torpedo while the
enemy ship is meters away from their position.
However, the ammunition is too heavy, falling on Van Praag's feet, which get crushed.
With the help of Jenga, the crew manages to load the torpedo in the hatch.
Stan orders Franz to fire, but the captain hesitates since he does not want to fight
back against fellow Germans.
Nevertheless, they fire directly at the enemy vessel and brace for impact as it returns
fire.
Luckily, the missile only scrapes the sides of their ship, while their torpedo makes direct
contact because the safety distance mechanism is disabled.
Though the enemy boat explodes, it sends a shockwave that blasts through their submarine,
causing a massive leak in the haul.
They return to the surface midway through a stormy night to drain the excess water.
Shortly after, the group tends to Van Praag's injuries while he loses lots of blood.
Stan instructs Fons to cut off his legs since he has previous experience butchering animals,
but he hesitates.
Filip takes the saw, volunteering to cut them himself, as the men strap Van Praag down and
keep him calm with alcohol.
Shortly after they recuperate from their harrowing experience, a German Destroyer arrives and
radios the crew to offer assistance, believing they are a German vessel floating off course
due to a repair issue.
Franz allows the German boarding party to inspect their boat since there is no option
to escape, much to Stan's anger.
He explains that they must keep quiet so they will not get suspicious that they cannot speak
German.
Not long after, the German Commander climbs aboard and heartily discusses their quest
to locate a rogue U-boat in the area with Franz, who offers his crew whiskey.
While drinking, they hear someone screaming in terror, prompting one of the German medics
to help.
Unfortunately, he discovers their ruse as Van Praag shouts in Flemish, alerting his
mates.
Chaos ensues as the men desperately eliminate the Nazi officers at the cost of Van Praag
and Werner's lives.
Stan is held at gunpoint but is saved by Franz, shooting the German Commander in the head.
They sulk for a moment, with Franz revealing he has heard rumors about uranium being key
in creating a weapon of mass destruction.
Believing that Germany must never find out about their cargo, he encourages the crew
to continue the mission.
Moments later, Franz spots the German Destroyer signaling their Commander to return to their
vessel.
Realizing they will retaliate soon, Stan hands a sniper rifle to Nadine, hoping she will
successfully shoot down the enemy vessel's deck gun.
Using the cover of darkness and heavy rain, Nadine climbs above the submarine.
She aims at the weapon, making a direct hit with the explosive bullets loaded in the ammunition.
However, the Destroyer rams itself onto its vessel, causing another massive leak that
forces them to sink underwater.
Klisse reluctantly closes the main hatch, leaving Tamme to drown after getting his watch
stuck on a lever.
Valves break apart due to too much pressure, causing the screws to fly out and hit Stan
in the liver.
Not long after, the ship sharply crashes into the rocky depths while Nadine gets stuck on
the other side of the haul due to a door blockage.
With time running out before the room floods, Franz signals for help using Morse code by
tapping on the pipes.
Though Stan is bleeding profusely, he blasts out of the submarine to swim toward the area
where Nadine is stuck.
Believing this is the end for her, Filip tearfully professes his love on the window as she watches
her drown.
Fortunately, Stan saves her and dislodges the door's barricade.
After some seconds, Nadine is resuscitated back to life, relieving everyone.
To protect the entire ship, Franz sacrifices himself to fix it while underwater.
He succeeds and stares at a photo of his youngest son before drowning.
Meanwhile, Stan gives Filip his wife's ring, reminding him it is not too late to marry
Nadine.
He dies peacefully in his daughter's arms.
Four years later, in August 1945, the surviving Flemish resistance group retired in Miami
Beach, Florida, with Filip and Nadine bearing children.
Overheard on the radio is President Truman's announcement that an atomic bomb successfully
decimated the island of Hiroshima.