Watch a report by ITV News Anglia's Russell Hookey
Boris Johnson at been at Colchester garrison in Essex visiting troops just back from evacuation operations in Afghanistan.
He paid tribute to soldiers from 16 Air Assault Brigade based at Merville Barracks in the town.
The Prime Minister said: "Mainly, I want to say what an incredible thing you've just done. There's literally nothing like it, not just in my lifetime, but I don't think this century or for the last 100 years or longer."
Mr Johnson said the operation was "nothing like the Berlin airlift" or other military evacuations, adding: "This wasn't just a military evacuation, this was the biggest-ever humanitarian airlift in the history of this country, and I don't think anybody expected that you would bring back 16,000 people.
"It was an extraordinary feat of endurance, patience, care, thought, planning, and I think you should all be incredibly proud of what you've just done and I know the whole country is incredibly proud of you for what you did."
Boris Johnson has defended his Government's response to the Afghanistan crisisduring the visit.
Asked why Foreign Secretary Dominic Raab was on holiday despite it being clear Kabul was about to fall, Mr Johnson told reporters: "I think the whole Government has been working continuously to make sure that we did what we could to extract people from Kabul.
"I think everybody who has taken part - I'm talking about the armed forces - in the Kabul airlift, and they've seen some pretty harrowing things and they've been exposed to people in the extremity of anxiety, of fear for their lives, and they've acquitted themselves incredibly well.
"I think they should be very, very proud of what they've done."