Mr Strong has been a firefighter with the New York City Fire Department for 36 years and now holds the rank deputy assistant chief.
Mr San Filippo is a battalion chief and directs foam and dry chemical operations citywide. He joined the department in 1978 after a three-year stint in the United States Navy.
Both men were at home when two passenger airliners hijacked by terrorist group al-Qaeda were deliberately crashed into the Twin Towers.
Within an hour and 42 minutes, both 110-storey towers collapsed. In total, 2606 people were killed, including 343 New York City firefighters.
"I had worked the night before, I watched most of it unfold on TV," Mr Strong said.
"After watching the second plane strike the tower I gave my wife a hug and a kiss and told her 'I'm going to work'. She said, 'What do you mean? You're not going to work' - but that's what I did."
Mr San Filippo had the day off but after hearing of the attack he also headed to his firehouse. "After both towers had come down it was our job to search the Winter Gardens [a building destroyed by the dust clouds triggered by the towers' collapse]. We were searching for life, for survivors.
"That was our day, we worked until about midnight.
"The city was a ghost town by that stage. We were in Manhattan and we had to get back to Brooklyn. There was no transport ... so we started walking. Then we saw a truck driving and we stopped him. There were about 20 of us and we basically commandeered it, that's how we got back."
Both men returned to work day after day, trying to deal with the enormity of what had happened in their city.
The day after the attack Mr Strong was assigned to the World Trade Centre.
"As I walked down I was just in disbelief at the amount of damage. There were still fires burning, it was still chaotic.
"We found one member of our squad. That was the only body we found ... "
Mr San Filippo said when "the list" of firefighters missing or dead started to come out it was overwhelming.
"There were 70-75 people that I had personally worked with. When things got under control we started to realise we were never going to see these guys again."
Among those they knew was a firefighter whose wife was heavily pregnant. She gave birth days after. Another colleague was killed on his birthday.
"He would have been 54 on Friday," Mr San Filippo said.
Both men think about 9/11 often but the anniversary is when it all comes back to them. Being in New Zealand for the anniversary this year was special for both of them.
It highlighted how the attacks on New York were a global tragedy, not just a US event. Climb organiser Tony Scott, of Auckland Airport Rescue, said it was important to pay tribute to the firefighters who lost their lives on that terrifying day.
"One of the [New York] guys who was here last year summed it up. He said it was the day the world changed forever. No one ever thought that could happen," Mr Scott said.
"It was a life-changing event for all of us."
A day to remember lost friends and family
The terror attacks on the Twin Towers are remembered as the day that changed the world forever. Photo / Getty Images
The Firefighter Memorial Climb has been held each September 11 in Auckland, previously at the BNZ Tower but this year at the Sky Tower.
Auckland Airport Rescue firefighter Tony Scott, who has been with the Fire Service for 22 years, said the event was a tribute to the 56 Kiwi firefighters who have died in the line of duty and the 343 fire service personnel killed in New York on 9/11.
"We need a day to remember our friends, a day to remember our fellow firefighters, who have in most cases been family," he said.
"The intention of this climb is for firefighters to participate as a shift, a watch or a brigade, and to climb together.
"Every fallen firefighter will be remembered by their name written out on a tally [name tag] the date they passed. Firefighters then ... carry the memory of the firefighter as they climb."
The event will begin with the names of the fallen being read - the New Zealanders by a local firefighter and the New York firefighters by Robert Strong and Steven San Filippo.
About 110 firefighters will climb. The maximum number of participants is 399 - representing 56 New Zealand and 343 FDNY firefighters.
The Firefighter Memorial Climb
• Friday September 11. • The event starts at 10am with a morning climb, a timed tandem event. • The memorial starts at 3pm. • 110 firefighters from New Zealand and New York will climb. • They are paying tribute to 56 Kiwi firefighters killed to date and 343 New York firefighters killed on 9/11.
