More than 300 events are being held across the UK to mark Armed Forces Day.
The main 11th annual event, which honours servicemen and women from all branches of the armed forces as well as veterans, is being hosted in Salisbury.
Thousands of people have paid their respects in the city, including the Princess Royal, who received a salute during a parade of more than 1,300 service personnel, veterans and cadets.
Rock band the Kaiser Chiefs will headline a concert later.
Also performing on Saturday are military musicians including the Military Wives Choirs and bands from the Royal Marines and the Royal Air Force.
The day is being celebrated with military displays, including a flypast by the RAF’s Red Arrows and an aerial display by the Army’s Parachute Regiment.
In a video on social media, Prime Minister Theresa May said: “Thank you to all of you who choose to serve your country whether Royal Navy, Army or Royal Air Force, full-time or reserve, the longest-serving veteran or the newest recruits.”
She also recognised the sacrifices family members of servicemen and women make.
“It is also a chance to remember the wider service community, whether it is children who endure long periods apart from their mothers and fathers, or friends and families who do so much to support loved ones in uniform,” she said.
The RAF’s leading charity, the RAF Benevolent Fund used the celebrations as an opportunity to call on the public for support.
It said there are more than 300,000 members of the RAF’s current serving personnel and veterans or their close families in need of support but not seeking it.
Air Vice-Marshal David Murray, the charity’s chief executive, said: “The selflessness and self-reliance needed to make these can often mean that our veterans don’t seek support, even when it’s available.
“We want to change this and reach veterans and their dependants who need help now, before it’s too late.”
Jeremy Corbyn, who met military personnel earlier this week, used the day to set out Labour’s plans for the armed forces, promising to treat them with the “dignity and respect they deserve”.
Conservative leadership candidate, Jeremy Hunt, also took the opportunity to thank service personnel and reaffirmed his pledge to “boost our defence by £15bn” if he becomes prime minister.
Boris Johnson attended a flag raising ceremony in Shropshire, and said it was “an honour” to meet armed forces personnel, who have “so selflessly served our country”.