A top US commander in Afghanistan says allied combat troops left Helmand Province "too soon".
Brigadier General Benjamin Watson is the most senior US general in Helmand and says the withdrawal left Afghan security forces with "more than they could handle".
In response to the question on whether he believes NATO combat troops, including the British, left too soon, he replied:
"As a military officer, I do.
"I know those are normally political decisions so I won't attempt to break that apart in this kind of forum. But from a military perceptive we absolutely left to soon."
He added: "We left the Afghan security forces with more than they could handle and I think we saw the catastrophic results."
The first US Marines were sent to Helmand in 2001, by Former President, George Bush in the wake of 9/11.
Former Brigadier General, Jim Mattis led 1,000 US Marines into the Helmand desert to establish America's first base there - at one point there were 20,000 Marines on the ground, in the country.
British forces handed Northern Helmand to the US Marines in 2010 - four years later NATO combat troops left the country and security was handed over to Afghan forces.
But by 2016 that security was fast evaporating.
Musa Qal’ah, Nad Ali and Sangin – the latter a town that cost a hundred British lives, were all back in Taliban hands.
Also, the provincial capital Lashkar Gar, once a British HQ, was close to falling.
In the town of Marjah, two battalions of Afghan troops were completely cut off and could only be resupplied by air. A small task force of US troops was urgently sent in.
Last April, a further 300 US Marines were sent back to Afghanistan to help train their army, with the aim to advise and assist Afghan forces to turn the tide against the Taliban.
Lieutenant Colonel Ryan Benson, Deputy Senior Advisor to the Afghan National Army, said:
"The 215th Corps, the 505th zone of the Afghan National Police, along with the Afghan National Civil Order Police and the Afghan Border Police, all went into offensive operations - kind of all hands on deck here in Helmand.
"They started to push out that security bubble."
Now, US Marines in Afghanistan are based inside Camp Shorabak, with most of these from the 8th Marine Regiment based out of Camp LeJeune, in North Carolina.
A mix of senior NCOs and junior officers have been using the regional training centre, where they are being taught how to become instructors.
Marine instructor Staff Sergeant Jeremy Plympton has been teaching the army:
"What I'm doing here is teaching them how to teach a class, because these guys have never taught a class before."
In the past few years Afghan forces have suffered crippling casualties rates - in 2016, 6,800 soldiers and police were killed.
Meanwhile, 2,500 lost their lives in the first four months of 2017.
The Afghan government no longer publishes the number of dead and injured.
Last year, three American soldiers were killed and 11 wounded in so-called green-on-blue attacks shot by rogue Afghan troops.
The mission of the Marines is now focused on training, but they do occasionally take part in combat operations.
In May, they used a rocket system known as the High Mobility Artillery Rocket System (HIMARS) to kill 50 Taliban leaders as they gathered in a compound in Musa Qal’ah.
Since the Marines arrived the Afghans have retaken Marjah and Nad Ali. Nawa District is also back in government hands and security has been widened around Lashkar Gar.
But monitoring groups say 43% of Afghanistan is still in Taliban hands or facing attacks from insurgents.
Seventeen years on, the mission in the country is still costing US taxpayers $45 billion a year.
After initially dismissing the idea, the Trump administration is reportedly now considering talking to the Taliban to try and break the stalemate.