Wisconsin native, 'Bachelor' star Nick Viall conquered survival tests and wrote a death letter to loved ones on Fox's 'Special Forces'

Warning: Spoilers from Season 2 Episode 6 of "Special Forces: World's Toughest Test" ahead.

A helicopter crash survival drill that involved being submerged into icy waters.

Switching on aggression to overpower another person — then turning it off at the drop of a hat.

And, writing a letter to loved ones as if you weren't going to survive.

These were the challenges Waukesha native and "Bachelor" franchise star Nick Viall and his fellow celebrity recruits were up against during Monday night's episode of Fox's "Special Forces."

On the show, celebrities take on "grueling challenges from the playbook of the actual Special Forces selection process" while battling the harsh elements of winter in New Zealand, according to Fox. The Directing Staff, made up of an elite team of ex-Special Forces operatives, leads the recruits through the course's demanding training exercises.

At the start of Day 6, seven recruits remained. Before day's end, that number would drop to six.

Here's a look at how Viall did during each stage of the day and if he made it to Day 7:

First exercise of the survival phase of the course: A helicopter crash survival drill

Ahead of the first challenge of Day 6, Billy Billingham, formerly of the British Army's Special Air Service, told the recruits that they were entering the survival phase of the course.

"In our world, you end up in situations you never want to be in," he said. "You are literally fighting to live. Fighting to win. Fighting to go another day."

The first exercise of the new phase — and day — was a helicopter crash survival drill. Billingham shared that DS agent Jason Fox, who was formerly a part of the elite Special Boat Services, had previously been in two helicopter crashes.

One at a time, recruits were placed in a helicopter that looked like it had been roughed up. It was suspended in the air above an icy body of water.

The helicopter was lowered into the water. The recruits tried to catch one big breath to hold right before going under. Once submerged, the recruits were to remain underwater for 15 seconds.

When a DS agent tapped the recruit on the shoulder, the recruit had to unbuckle their safety belt and retrieve an onboard life jacket. Then, they could return to the water's surface.

As Viall was being lowered, a DS agent said: "He's panicking in there." But, Viall would become one of the five recruits to pass the test.

Olympic speed-skating champion Erin Jackson panicked and failed the exercise. And, media personality Jack Osbourne, who has multiple sclerosis, was under medical supervision for a fast heart rate and missed the challenge. Osbourne was told he had to be medically withdrawn during the episode, which meant his time on the show was over.

When the DS was privately discussing the recruits' performances from the drill, chief instructor Rudy Reyes, a former recon marine, said Viall was "very composed."

"He looked worried. He didn't act worried," Billingham said.

The recruits' will to fight for survival was tested. Here's how.

The recruits' will to fight for survival. That's what the second challenge of the day was designed to test.

Reyes instructed them to "switch on" their aggression and overpower whatever was behind a gate they were standing by. And then, turn their aggression off right when the DS commanded them to.

"In our world, we need to be able to go from calm to completely in the red in the snap of a finger," Reyes said.

Waiting for the recruits behind the gate was DS agent Jovon “Q” Quarles — wearing red protective gear — who they would fight one at a time. The only thing off-limits was headshots.

"You think about what you'll fight to the death for," Reyes said. "Those dreams that you have, that family that you have, those hopes about yourself. Think about what you fight to get back to."

When Viall was up, he came out swinging. He used his body's force to get Quarles on the ground and kept hitting him.

"Being here, there's a part of me that wants to test my ability to protect my family," Viall said during a cutaway.

Afterwards, Billingham talked to the recruits individually about their mindsets during their fights.

"I want to be there to raise my child," Viall told Billingham. "I would destroy anything that came in my way of that."

"OK, well done," Billingham replied. "Good effort."

Recruits had to write a death letter to their loved ones and read them aloud

"If you go on deployment as a Special Forces operator, you know you're going to possibly get killed," Quarles told the recruits. "Y'all want to know what it's like to be us. This is what it is."

The recruits were instructed to write a death letter to their loved ones as if they weren't coming home. Then, they had to read them aloud to their peers.

"Some of the things that we put the recruits through on this course may seem absolutely brutal," Fox said. "But there is a reason for it. War is relentless. It's obviously physical, but I'd say 70% of it is mental."

Viall was already fighting back tears when it got to his turn to read.

"To my fiancée Natalie: Having you by my side always gave me the courage that I could face any challenge because I had you," Viall read. "I'm so sorry I won't be there. I'm so sorry I won't be with you to raise our baby together. You're the greatest love of my life."

Viall and his fiancée, Natalie Joy, shared their engagement on social media in January. Over the summer, the pair announced they were expecting.

During last week's episode, Viall revealed that his motivation on the show comes from becoming a first-time dad.

Six recruits, including Viall, made it to Day 7. The next episode will air at 8 p.m. CT Monday on Fox.