As the door opens, all the trainees freeze. A man strolls in, his steps slow and measured. A pair of dark sunglasses is perched atop his sharp nose. He has an aura of confidence that demands respect.
"Isn't this good?" he asks, his tone as impassive as the expression on his face. "I size you up, you size me up."
For the 39th Batch of NDU trainees, that was our first encounter with 3WO Seah.
Having graduated from Basic Military Training three days earlier, we were now immersed in a far greater challenge - the 16-week Combat Diver Course (CDC).
As we navigated the next four months - which were the most difficult, revealing and rewarding of my life - the man we called "Warrant Hans" was our guide.
You have to stay strong
He demanded our best in everything we did. Once, a trainee completed his IPPT (Individual Physical Proficiency Test) 2.4km run in 7min 43s.
Warrant Hans immediately "dropped" the trainee for 50 push-ups, because he had failed to surpass his previous timing of 7min 38s.
Warrant Hans was not being cruel - he wanted to make us stronger, to show us that only by pushing ourselves could we improve.
On one occasion, he revealed: "There is a purpose behind everything I say or do. You might not see it, but it’s there."
He could be fierce and unwavering, but he was also an unflinchingly fair man. When we deserved it, he showered upon us seemingly endless waves of push-ups, flutter kicks, and other muscle-searing exercises. He never "hammered" (punished) us without reason.
On the flip-side, if we performed well, he did not hesitate to praise. For this, he commanded our undying respect.
As time went on, we began to catch glimpses of warmth and laughter beneath his steely facade.
Gradually, his true personality trickled through, and we learned that he was a family man, devoted to his wife and two children; a quipster capable of effortlessly making us laugh; and a motivator, inspiring us to transcend our perceived limits.
You gotta tough it out
Often, after a gruelling session of physical training, he talked to all of us as a batch.
In these talks, he encouraged us to highlight any issues we had, and helped us to solve them. If he sensed our dedication was waning, he could revitalise our resolve.
When one trainee expressed uncertainty as to whether he could survive the course, Warrant Hans answered: "To see the rainbow, you have to get through the rain."
Our training was his top priority, and he frequently worked late. One night, as he was helping us plan a simulated mission, he received a phone call from his daughter. He placed it on speaker, and we heard his daughter ask when her daddy would be home for her birthday.
With disbelief, we realised that Warrant Hans was spending her birthday working with us. As we sang Happy Birthday to his daughter, we truly understood the depth of our Platoon Commander's dedication.
On 20 Sep 2013, the 39th CDC batch graduated. Under Warrant Hans' stewardship, a record-breaking 73 trainees passed out as naval divers. The norm is around 50.
You must do your best
Shortly afterwards, I learnt I would be one of five divers sent to Officer Cadet School. Though incredibly honoured to be chosen, I was reluctant to leave.
It was heart-wrenching to leave my batch, to leave NDU. Asking Warrant Hans if we could talk privately, I voiced my feelings.
In response, he did not offer compassion or consolation. Instead, he simply said: "If not you, then who? You have a responsibility to go - to represent 39th, to represent NDU."
Standing before the man who led us through so much, I was suddenly gripped by a memory. It was of Warrant Hans speaking to us midway through CDC.
He said: "I am very protective of my family. You all are my family. I will stand in front of you all - when the heat is coming, I will stand in front of you. I represent you.
"And, rightfully so, you must represent me."
Warrant Hans' hawk-like gaze, as piercing as ever, bore into me.
I nodded, and said the only thing I could.
"I'll do my best, sir."