For 17-year-old Titmus, it will be her first Pan Pacific Championships, something she is excited to experience.

"Really excited, it the first time I've ever been to Tokyo and I think it will be a smaller team compared to Commonwealth Games so I'm looking forward to that and getting to race to the Americans," she said.

Titmus burst onto the world stage when she made a blitzing 800m swim at the Commonwealth Games in April and set the fourth quickest time (8:20.02) in the last 15 months.

Since her Commonwealth Game trials, Titmus has drawn comparisons to Ledecky, who has looked untouchable over the 400m and 800m freestyle events since the 2012 London Olympics.

Ledecky was only 15 at the time when she broke the American Record by swimming the second fastest time ever, behind Rebecca Adlington's world record of 8:14.10 set in 2008, in the 400m freestyle final.

"I want to see where I am up against her," Titmus said.

"If there was no one else I was chasing, I wouldn't be swimming as well as I am right now.

"She is someone to chase and work towards," she said.