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The troops from Norton Manor Camp will be serving in Sangin in Helmand Province until November.
Before they left Heart went to speak to some of them.
We asked Commanding Officer Major Sean Brady what exactly our Marines would be doing over there...
"On a day to day basis my guys will be on the ground with the Afghan National Army and the Afghan National Police. What we're aiming to do is protect the local population and develop the Afghan security forces. But we all know the insurgents out there are going to try to prevent us to do that so our job will be to stop them"
Its Captain Dominic Rogers' first time in Afghanistan - he told us he'll have a specific job to do out there...
"It's about developing the capability and the confidence of the police in Sangin where we're going to be based to do their job so its very important indeed. The overall goal is to leave the security for Afghanistan over to the Afghans and developing the police to be able to do that themselves is very important"
The last time 40 Commando were in Afghanistan back in 2008, 3 of their comrades - Corporal Damien Mulvihill, Marine David Marsh and Lieutenant John Thornton - were killed in action.
We asked Captain Rogers if this was affecting the way he felt about his mission...
"Obviously there's a great sadness about the loss of 40 Commando ranks from the last tour. All the other battlegroups who've gone out, particularly to Sangin, have all had their casualties. But I think we've got to concentrate on the job we have to do and keep that in the forefront of our minds"
Lance Corporal Ray is a 40 Commando medic - he told us about the medical training all the troops have had to do...
"We've been doing medical scenarios and training the guys in immediate primary care for any casualty - applying tourniquets and opening airways up. We're pretty much 100% for the whole unit, which i dont think has been done before, so medically I think we've got a really good starting chance"
And there was one intensive course on how to treat someone after an explosion which Lance Corporal Ray told us was tough going...
"For the guys, its a bit of a shock, we use a company called Amputees in Action and they've got real amputees who dress up. I think the first time the guys saw that, its just a bit more realism but thats exactly what you need for the training"
There's also plans to create a memorial garden at the Norton Manor base whilst 40 Commando are away.
The bare bones of the garden are already there but its hoped by November a special centrepiece with a plaque will have been put up remembering fallen comrades.
Lieutenant Stuart Harrison told Heart the idea came from the families of fallen marines but its there for those at the base as well...
"I think its very important for the guys to have somewhere to go. They do think about fallen friends or they like to go somewhere for some quiet time. I've seen people there already even though its in its elementary stage at the moment so they do want it"
If you want to help out with fundraising for the garden please contact Heart on 01823 368330 or at email@example.com and we'll put you in touch with the right people.
Heart Somerset wishes the best of luck to our 40 Commando and is looking forward to welcoming them back safely in November.