The Territorial Army has celebrated its centenary with a pageant, re-enactments and a march along The Mall in London.
But the event was tinged by sadness over the loss of three TA members who were killed this week in Afghanistan.
The TA commemorated its achievements over the past 100 years at the event in Horse Guards Parade in London.
The Prince of Wales, the Duchess of Cornwall and the Earl of Wessex joined some 6,000 spectators to mark the reserve force's history.
'Risk is high'
Armed Forces minister Bob Ainsworth, who attended the event, said: "Without the support of their families, friends, and employers, the distinguished role the TA has played over 100 years would not be possible."
SAS reservists Corporal Sean Robert Reeve, Lance Corporal Richard Larkin and Paul Stout died on Tuesday along with regular soldier Corporal Sarah Bryant - the first British woman to be killed on active service in Afghanistan.
A senior officer in the Territorial Army, Brigadier Greg Smith, told the BBC that any loss was a shock but that the Territorial Army was "an army".
"And throughout our existence, on an operation, of course, you are always there with the knowledge that the risk is high of taking casualties, and ultimately some people pay the sacrifice," he said.
Chief of the General Staff General Sir Richard Dannatt, also a guest at the event, said he "saluted" every TA man and woman.
"Nearly 15,000 territorials have served in Iraq and Afghanistan alongside the regular Army since the start of the current campaigns.
"And it is a sad fact that in this time 11 Territorial Army soldiers have paid the ultimate sacrifice and laid down their lives - three this week in Helmand."
Sir Richard said the task at hand remains.
"But with their memory and sacrifice very much in mind the work nevertheless goes on."
Lance Corporal Darren Dixon, a bus driver from Edinburgh, said that despite the dangers, being part of the TA could be extremely fulfilling:
"There was the sense of adventure - the camaraderie - amongst the TA chaps, so I volunteered myself to go to Iraq and found myself in a bit more action than I thought I would be.
"I think it's natural for anyone to be worried about going to a war zone but if you have the inclination to join in the first place there's the sense of camaraderie there that will get you through it, and the training is second to none."
The ceremony included a march past St James Palace, where Prince Charles received the royal salute.
The prince is hosting a reception at the royal residence for serving and past reservists, representatives from Cadets Associations and employers whose staff serve in the TA.
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