Mr Judson's awards, which include the Distinguished Conduct Medal, the Military Medal and the Victoria Cross, were all won in a little over a month between July and August 1918 while he was serving in France.
He won his VC in Bapaume after he led a bombing party under heavy fire to capture an enemy machine-gun post. He then headed up a trench alone, bombing three machine-gun crews before he stood on the parapet and ordered the enemy party to surrender.
They instantly fired on him. He in turn threw a bomb at them, killing two and causing the rest to flee.
"One of the sirs told me he was one of the bravest soldiers ... It was pretty cool, I am very proud," said Mr O'Brien.
Mr Judson's medals were among the 96 stolen from the museum last December in a brazen theft that appalled the nation.
Mr O'Brien, who is nine weeks into his basic Army training, was happy police had made some arrests and the medals were to be returned to the museum. "It was a stupid thing to do, they deserve everything they get thrown at them."
Today, rows of Mr O'Brien's fellow recruits will welcome dignitaries and guests as the medals are returned - but he won't be among them.
He has another role, closer to his heart. "I'm taking my great-great-grandfather's medals back to the Valour Alcove where they belong."
Waiouru Army Museum director Colonel Raymond Seymour said the return of the medals was a huge relief.
He would not say what security changes had been made since the break-in, although the roller doors and security cameras in the Valour Alcove gave some clues.
"It's a day we've been waiting for for a long time," Colonel Seymour said. "I really couldn't describe the issues or emotions we've all been through, but let's make it quite clear, these medals are the nation's treasure."
