Theresa May has paid tribute to the "valiant" servicemen and women who help keep Britain safe in her seasonal message to the troops.
She said she is "immensely grateful" for the sacrifice of those who cannot be home for Christmas.
The Prime Minister also recognised the sacrifice of parents and children who often have to change their school or job and cope with long periods apart from their loved ones.
May recognised the work done by Britain's armed forces training Iraqi forces as they fight Islamic State, the RAF's bombing campaign which has helped shrink the militants' influence in the region, and the Navy's work bringing disaster relief to those hit by Hurricane Irma in the Caribbean.
And she highlighted the work of troops who were twice deployed on British streets following terror attacks at home.
"Whenever you are called upon - regulars or reserves - you always give of your best and inspire us all with your service," she said.
The PM drew attention to the military covenant, which ensures servicemen, women and their families are treated fairly.
"Partners and children are often called on to make huge sacrifices of their own - from a change of school or job, to coping with extended periods of separation," she said.
"That separation is especially difficult at Christmas time, and we should all be immensely grateful for that sacrifice."