The Prince of Wales has paid tribute to the great "personal sacrifice" of Britain's servicemen and women in a Christmas message to the armed forces.
Charles spoke of his admiration for those who endure "great danger" to protect the country, and the families who support them.
And he praised the "professionalism, understanding and cultural sensitivity" of those in the military.
Delivering the address to Forces TV and BFBS (British Forces Broadcasting Services) Radio, he said service personnel will face many challenging tasks over the festive period, some of which will "put our service people in great danger as they carry out their challenging duties".
He said: "I am delighted to have this opportunity to send you all a Christmas message, for while many of the current news headlines around the world appear rather grim, they have reminded us all of the vital importance of the armed forces.
"Sometimes it would appear that there is no real threat facing Britain and that therefore defence can perhaps seem somewhat irrelevant.
"However, the extent of current global deployments of the UK's armed forces only goes to highlight the continued, essential role of the armed forces in today's society."
Almost 23,000 military personnel will be stationed or deployed abroad over Christmas, including more than 3,000 on operations.
Of those, 870 are involved in the campaign to counter Islamic State (IS) and 200 are carrying out training in Iraq.
This month, HMS Defender and its 180-strong crew joined the French aircraft carrier Charles de Gaulle in the Indian Ocean to support operations against IS.
The Type 45 air defence destroyer is on a nine-month deployment to the Middle East and is set to continue with the French Carrier Task Group well into 2016.
There are almost 14,000 troops across Europe, including just over 3,000 in Cyprus, 1,170 across North Africa and the Middle East and about 1,000 in the Falklands.
Charles also thanked the families of those stationed across the globe, saying their "loyalty and constant support are such a crucial part of the remarkable selflessness of the whole military family".
He ended his message: "I can only wish you all the happiest possible Christmas and send you a sincere and heartfelt thank you for your continued service and personal sacrifice.
"I can assure you, ladies and gentlemen, that this is hugely valued and appreciated."