One hundred Royal Australian Navy soldiers lined the forecourt of the Opera House to mark 100 days until the International Fleet Review in Sydney Harbour, commemorating the arrival of the first naval fleet a century ago.

Ships from more than 20 nations and more than 8000 naval personnel will help celebrate the navy's historic event with a parade, fireworks display and light show to rival Vivid Sydney.

International Fleet Review director Captain Nick Bramwell said the Opera House would be lit up spectacularly.

"That's one of the reasons we are at the Opera House today - because it is part of the show," he said.

"They are major events that bring the navy family together. We're bringing in ships that aren't normally in Sydney so it's very important to us."

Wet weather prevented the naval helicopter from flying the giant flag over the Harbour but Captain Bramwell said everyone was in high spirits.

"We've actually found some initial descendants from that first fleet serving in the navy today and the sailors and officers are very proud of that history," he said.

The International Fleet Review will start with the 17 tall ships entering Sydney Harbour followed by a fleet entry of more than 25 warships.

Soldier Carly Boyd said the event brought back memories of her time on HMAS Darwin, which visited Sydney in 2009. She said: "It's going to be amazing. I can't wait."