More than 5,000 sailors, soldiers, airmen and marines will be working over the festive period, involved in 25 operations in more than 30 countries ranging from Iraq to the South Atlantic.
Where Are Our Military This Christmas?
Thousands of military personnel will be working on Christmas Day in locations around the globe - including Iraq, Afghanistan and the Falkland Islands.
In the South Atlantic, over 1000 personnel are stationed in the Falkland Islands.
In Afghanistan, troops from the Army and other Services are training Afghan National Security Forces.
Around 1,000 people are working to fight Daesh and train the local security forces from locations in Iraq and the wider Middle East as well as from RAF Akrotiri, Cyprus.
UK Air Component Commander, Air Commodore Roddy Dennis, based in the Middle East said: "Even though we are away from our homes, families and friends this festive season, we will all be celebrating Christmas in traditional Armed Forces’ fashion together with personnel from across the Coalition.
“I would like to thank everyone under my command for their service and everyone at home for the support they continue to give us, our mission would be impossible without it. We wish you all a very Merry Christmas and a happy and prosperous New Year.”
Royal Navy On Christmas
Naval yuletide traditions include officers serving the ship's company and lower ranks Christmas lunch.
The crew will often take crackers and presents from family and friends out with them, stowing them away until December 25.
In the Caribbean, RFA Mounts Bay joins other Royal Navy warships also deployed over the festive period.
Nearly 400 troops are providing engineering and medical assistance to the United Nations mission in South Sudan (UNMISS), in both Bentiu and Malakal.
It is one of the UK's largest deployments of peacekeeping troops around the world, and enables UNMISS to protect civilians, allow humanitarian access, monitor and investigate human rights abuses, and support the peace agreement.
Nato's Enhanced Forward Presence (eFP)
UK armed forces are taking a central role in the eFP - with the British Army currently leading a multinational battle group in Estonia.
The eFP in the Baltic states is a deployment of defensive, but combat-capable forces in countries which also includes Latvia and Lithuania, as well as around 150 UK personnel working in Poland.
Defence Secretary Gavin Williamson said: "I'm proud to have met our inspirational personnel here in Poland making such an important difference alongside key friends and partners like Poland and the United States.
"I'm so grateful to our brave men and women in the Armed Forces, working around the clock to keep us safe while so many of us spend time with friends and family over the Christmas period."
More than 800 British personnel are currently stationed in Estonia alongside Danish, French and Estonia forces with the 1st Battalion The Royal Welsh currently providing the bulk of the force.
Supporting units include The Queen's Royal Hussars, Royal Artillery, Royal Engineers and Royal Logistic Corps. A Light Cavalry Squadron, of 150 personnel, is also in Poland, as part of a US-led Battlegroup.
Around 70 personnel are taking part in a United Nations mission to train African Union and Somali National Army forces who are fighting an insurgency being waged by the Al Qaeda affiliate, al-Shabaab.
Royal Air Force (Quick Reaction Alert) On Christmas
QRA crews can take off within minutes to intercept aircraft and are ready to do so 24 hours a day, 365 days a year.
Wing Commander Andy Chisholm, a QRA pilot based at RAF Coningsby in Lincolnshire, said: "Really, it is broadly similar to any other day.
"We keep things just the same ... and we don't do anything different just because it is Christmas.
"Any alteration or change has the potential for distraction or confusion."
But the 40-year-old pilot, who has been in the RAF for 17 years, said there is a tradition that sees officers marched to the other ranks' mess.
"We are invited in, but we have to sing for our supper - we have to sing carols at the front door, and only once we have achieved the correct standard of singing are we allowed in to join them," he said.
The Household Cavalry Mounted Regiment On Christmas
Made up of the Life Guards and the Blues and Royals, and providing the Queen's Life Guard for the official entrance to the palaces, the regiment's daily duties have remained unchanged since 1660.
"It is very much like any other day - we do this 365 days a year," said Corporal Major Andrew Preston of carrying out guard duty at London's Horse Guards on Christmas Day.
"But what we try and do is make it a little bit enjoyable for the soldiers - we put a good breakfast on for them in the morning, the soldiers do a fancy dress guard, and there's lunch."
The troopers come up with "witty" fancy dress ideas, he said, with previous examples including a knight, a Victorian soldier and a muck pile.
And instead of being judged on 45 different inspection points - the cleaning standards of their horse and kit - on Christmas Day the soldiers are marked on their costume.
He said the "better the fancy dress, the better relief they get down at Queen's Life Guard".