Burton-on-Trent - Goalkeeper Jack Butland says a surprise trip to a military boot camp with the England squad had been "one of the most rewarding experiences I've ever had".
England manager Gareth Southgate surprised his players when they reported for international duty last Friday by whisking them away for a weekend at the Royal Marines' Commando Training Centre in Devon, southwest England.
The squad and key members of back-room staff spent 48 hours in military fatigues and carried out challenges such as camping out overnight and completing a gruelling obstacle course.
"It was tough, but it was one of the most rewarding experiences I've ever had," Stoke City goalkeeper Butland told reporters at England's St George's Park training base in Burton-on-Trent on Tuesday.
"We got to experience their way of life, the way they do things, their values and just how tight-knit they are as a family. I think as a squad and players, we all benefited from that.
"The Marines talk about something called disconnected expectations, which is the shock factor.
"It's being taken out of your comfort zone and being able to perform as well as you can do when you're at your most fatigued.
"That was something that was big for us and being able to pull together."
Southgate told the Football Association website: "We wanted to come and put the guys into a different environment, something they weren't expecting.
"We wanted to expose the guys to an elite environment with one of the elite forces in the world. We wanted them to see that there's another world out there."
England play old enemies Scotland in a World Cup qualifier in Glasgow on Saturday before ending the season with a friendly against France in Paris on Tuesday.