The track from Picton to Kaikoura was severely damaged, which required most of it to be completely ripped out, new formations created and tracks laid.
Searle said nothing could have prepared him for the job ahead.
"Some of it was six metres in the air, or sitting in paddocks, bridges were knocked out. A lot of the slips are still hanging there.
"I don't think any amount of training could prepare you for that. I mean the track was munted."
The team worked southwards while another team was moving north from Kaikoura to meet them at Ohau Point.
It was the "race to the tunnel", Kilgour said.
"Our main purpose was to beat those Kaikoura boys. Sort of like a rivalry, aye, Canterbury v Otago. We smoked 'em."
To do so they endured long slogs, including some 14-hour days, in sometimes stiflingly hot conditions.
"Coming from down south, we're lucky to get over 30 [degrees Celsius] one day a year," Kilgour said.
"But six in a row, combating the heat, you can't sleep at night. It was real rough."
As well as scorching heat, there was occasionally heavy rain.
John Kenata, the contracted digger operator of the group, became the hero of the day during a flash flood at Ohau Point in April as he was moving along the tracks on his high-rail digger.
"I looked back and a big lahar came across the road. I came around the corner and there were trucks all blocked up on the road."
He took his digger off the tracks, "trundled up to the road", and started clearing the muck.
"But as fast as you're clearing it, it just keeps coming down."
He managed to get the operator of another digger to help him, as well as three trucks, and as the rain eased they were able to clear the way.
The earthquakes were not over, Searle said — a new shake could ruin the day's work.
"Then we'd have to do it all over again."
Initially, they spent 10 days there, followed by four days off, during which they could return home.
After Easter, that increased to 26 days on, four days off, which was hard on the crew members, many of whom had young families.
Kilgour said he and his wife adopted a baby girl during this period.
"So it's really nice to be back now. You come home and she's got a smile there for you."
Sandy Schroder had a similar experience with his baby boy, who recently turned 1.
"So I missed nine months of his growing up."
The work itself varied hugely from day to day and finding materials for the massive undertaking became a major difficulty.
They would use whatever they could find, Searle said.
"We were getting it out of scrap. There was a yard in Blenheim which we cleaned out of what we needed."
The days were passed with banter, much of which was not suitable for broadcast.
"We were just good mates really," Searle said.
"We have a laugh together. There aren't many days where you can't have a laugh, often at others' misfortune."
Kilgour said the locals were incredibly welcoming, but seemed frustrated at the lack of progress from the Government in fixing their area.
"The main thing was roads for them. It was a bit disheartening that we were out there every day fixing the railway track and all they wanted to know is when the road's going to be open."
When asked what they did to entertain themselves, the crew was tight-lipped. Apparently what happens in Marlborough stays there.
"Work," Kilgour joked.
The rail gang returned to Dunedin last month.
Aitken left a shift earlier than the others to get home in time for the birth of his first child.
Searle said there were still parts of the track which needed finishing, such as temporary lines which had to be moved on to bridges once they were constructed.
However, there was definitely a huge sense of accomplishment, he said.
This sentiment was shared by their boss, Brian McAllister.
"I've seen what they've done and they've done way above what we were sent there to do.
"They needed to come home; they've been away far too long."
