A £15.7 million visitor's centre will be an "exciting new addition" to the National Memorial Arboretum, the Duke of Cambridge has said.
Building work on the memorial garden's Remembrance Centre has already started, but today there was a ceremonial breaking of the ground.
Prince William, the project's patron, said: "I am delighted that work is now to begin on building the new visitor centre.
"The Arboretum is a place of sanctuary, but also a place of education and those who visit deserve to be looked after when they are here."
The Prince was unable to attend in person, but had his words read aloud by another supporter, the TV star Dame Penelope Keith.
He added: "I am grateful to the National Memorial Arboretum management team and the Appeal Council for working so hard to make this visitor centre possible.
"In just over a year's time, the project will be complete - an exciting new addition to this very special place - and I look forward to seeing it in person."
During the ceremony, Dame Penelope and young sea cadet Beth Molyneux each took a hand on the spade, to dig a symbolic patch of earth near what will eventually be a landscaped area known as Heroes' Square.
The 10-year-old girl also read a touching poem about why she wears a poppy, in memory of her father Lieutenant Commander Ian Molyneux.
He was fatally shot aboard the nuclear-powered submarine HMS Astute while docked at Southampton in 2011.
The naval officer was killed by Able Seaman Ryan Donovan, who was later jailed for life with a minimum term of 25 years after admitting murder.
The arboretum, made up of more than 300 monuments including the centrepiece Armed Forces memorial, has welcomed growing numbers of visitors since opening at Alrewas in Staffordshire in 2001.
When first proposed, fewer than 100,000 people a year were expected - but with growing public awareness and recent conflicts in Iraq and Afghanistan, triple that figure now visit annually.
The Royal British Legion, which runs the 150-acre site, is hoping the new centre will cater for half a million visitors each year, educating people about British and Commonwealth service personnel killed on active service since the Second World War.
Dame Penelope said the arboretum was "a remarkable place", allowing visitors to pay respects to those who have made the ultimate sacrifice.
She said: "We tend to concentrate on the Cenotaph - quite rightly so - and the dead of the two enormous wars, but it's to remind people servicemen do go on working, and die as well.
"I came up here before the memorial was put in place, and have seen it over the years grow and grow. I think it's a remarkable place."
Dame Penelope, who has supported the arboretum since it's inception, said: "It's a garden and gardens do amazing things; to remember, to celebrate, to mourn - and the fact that it's growing, that's good.
"These people have given their lives, but they have something that commemorates that, that is growing, and I think that is the beautiful thing about it."
The RBL's national president, Vice Admiral Peter Wilkinson, said: "The arboretum has rapidly established itself as part of the national consciousness.
"It is a source of great pride for our nation and we are pleased to mark this vital step in its further development."
So far, more than £10 million of the money needed has been raised from various sources including private donors, Staffordshire County Council and the Heritage Lottery Fund.