An impression of how the arboretum's new entrance could look
Volunteers at the National Memorial Arboretum in Staffordshire have said facilities at the site are becoming inadequate due to its popularity.
A spokesman said they were being forced to hold events in muddy fields and host veterans in semi-permanent marquees.
The Arboretum, home to the Armed Forces Memorial, has launched an appeal to raise £8m for improvements.
Next year, it will also become home to the Basra Wall - a memorial dedicated to those killed in Iraq.
The comments came as the centre showed off architects' designs of its newly-planned buildings.
Major General Patrick Cordingley, commander of the Desert Rats in the first Gulf War and chairman of the appeal, said he had not met anybody who had not been moved by a visit to the arboretum, which is based in Alrewas.
"Such is the popularity of the arboretum, especially around Remembrance time, that we're now forced to hold major events on a muddy field and host veterans in semi-permanent marquees.
"It's not good enough and we must better honour the memory of those who have gone before us," he said.
The appeal was launched in April by Prince William who has agreed to become a patron.