BARCELONA - Missy Franklin has been dubbed America's swimming 'Wonder Woman' after claiming her fourth gold at the world championships by anchoring the USA team to victory in Thursday's 4x200m freestyle relay.

Franklin, 18, powered down the pool in the final leg to clock 7min 45.14sec for the USA, the Olympic champions, with Australia finishing second at 1.94 back and France taking bronze at 3.29 adrift. It was an exact repeat of the medallists in the London 2012 Olympic final.

Australia's Cate Campbell, one of Franklin's main rivals in Friday night's 100m freestyle final, has said the US star is swimming like an All-American superhero. "Missy has shown that she is Wonder Woman," said Campbell. "She is already wearing lycra, she just doesn't have the cape!" With 16-year-old Katie Ledecky, who smashed nearly six seconds off the world 1500m freestyle record on Tuesday, swimming the first leg, a USA victory had looked like a foregone conclusion, something Franklin rejected.

"We don't even think about that stuff," insisted the teenager. "My motivation speeches consist of just saying 'go out there and have some fun' so that's what we do. Being up there and singing your anthem completely out of key at the top of your lungs is when you know the hard work has paid off!" After gold in Sunday's 4x100m freestyle relay with the USA team and her individual victories in Tuesday's 100m backstroke and Wednesday's 200m freestyle final, Franklin has claimed four of seven possible golds in Barcelona.

Despite her haul, Franklin has no time to celebrate as she races again in Friday morning's 200m backstroke heats, then the evening's hotly-anticipated women's 100m freestyle final. Franklin, a backstroke specialist, will be up against 50 and 100m freestyle Olympic champion Ranomi Kromowidjojo and world leader Campbell, plus world 50 and 100m freestyle record-holder Britta Steffen of Germany.

"I absolutely will celebrate eventually, but you just have to take it one race at a time and enjoy it one at a time," said Franklin, who is racing on a daily basis in Barcelona. Ledecky was delighted after collecting her second gold medal following her 1500m freestyle triumph.

"It was such a great experience to be with all these girls and it is definitely the most fun I have ever had in a race," said the teenager. Australia's Bronte Barratt, who swam the first leg, said her team were happy to add world silver to their second place at the Olympics. "I think it is a very good sign for us to back up silver at last year's Olympics with another silver here," said Barratt.

"A few people have said to me this week that this year isn't the time to win gold medals. We're still three years away from Rio which is the ultimate goal." With Franklin as the dominant force at these world championships, Kylie Palmer said the Australian quartet had done well to compete with their American rivals. "It was always going to be so hard to be up there with USA, especially with Missy going last, so I think we did a good job just to be up with them tonight," said the 23-year-old.