The picture shows an American soldier in a bunker in Afghanistan's Korengal Valley during fierce fighting with the Taleban.
I was working with the writer Sebastian Junger on assignment for Vanity Fair on a year-long project with Battle Company of the US 503rd Airborne Battalion.
We were based in Korengal Valley in Afghanistan's Kunar province, towards the border with Pakistan.
The area is considered to be the epicentre of the US forces fighting in Afghanistan and one of the most deadly. A place where the combat is often at close quarters.
The platoon was based at a rocky outpost called Restrepo, named after a US medic who had died. The fighting in this region is pretty intense, I was quite surprised.
I hadn't expected it to be so heavy but in this area you can expect to engage the Taleban at least once per day.
The outpost consists of a sandbagged area approximately 30m (98ft) long and 10m (32ft) wide, with a bunker at one end. The aim of the position is to protect the main US base further up the valley.
'Everyone was exhausted'
The day this picture was a pretty intense day. We'd already had two engagements with Taleban or foreign fighter insurgents in the area, and they had established a line of fire inside the base.
As the picture shows, everyone was exhausted. One guy had to jump into the base and broke his leg, requiring a medical evacuation by helicopter later in the night.
We later received a radio communication that a supply of grenades and suicide vests had entered the valley. We were perched on the hillside in this valley fearing the enemy had come to the perimeter of the bunker, maybe 30 meters or so and might attempt to overrun us. Let's just say we were concerned.
In the spring, another American base in Nuristan was on the end of a concentrated attack. US troops ended up calling in air support on their own compound to survive. With that fresh in our minds it wasn't impossible to contemplate the idea of being overrun.
At the time I took the picture, I remember seeing the image on the back of the digital camera back showing it to Sebastian. I knew it was good. I couldn't scroll through the pictures because of the light emitted from the camera could be seen at night and therefore could put us in danger.
I remained in the valley for another week or so, and then came back to the US, before returning for another operation.
I then broke my leg on a combat operation in October while coming down a mountain. I had to be operated on in Bagram, and since then I've been recovering, before going back in April.
Winning the top prize in the World Press Photo Contest garners attention like no other photo award. I've won prizes in the Contest before, but not the main one. You can't put yourself in a position to win the top prize; it's such a chance thing.
In the end, Vanity Fair didn't use this picture in their publication. We tried to use it as the opening spread, but it didn't work as well as the edit we finally chose.
I'm committed to this project. I wouldn't characterise myself as a press photographer, more a documentary one, working on long-term projects.
The beauty of this assignment is that in January Vanity fair ran 10-12 uninterrupted pages of our work from Afghanistan - it's not often you can get that kind of exposure.