Former champions Williams hope the last could be first again after finally unveiling their 2013 Formula One car at the Barcelona circuit where they were winners last year.
The last of the 11 teams to show off their new car, Williams hoped the FW35 would be an improvement on the FW34 that took Venezuelan Pastor Maldonado to their first victory in nearly eight years last May.
"Given the rule stability over the winter, I'm pleased with the gains that we've been able to make with this car," said technical director Mike Coughlan in a statement for the rollout at the Circuit de Catalunya.
"It's a better, more refined Formula One car than the FW34."
Founder Frank Williams, whose team are the second most successful in Formula One in terms of constructors' championships (nine) but finished last year in eighth place, see better times ahead.
"We will have to wait until Australia to truly see what we have, but we believe it is a step forward from last year's car which was also a very competitive vehicle," he declared.
"Williams has been at the top many times over the last 30 years. It's the nature of the sport to have ups and downs, but when we are down we always fight our way back.
"I'm hoping that with the current team we have in place... we will be in a position to challenge the very best."
Maldonado has a new team mate this year in Finnish rookie Valtteri Bottas, previously the reserve.
Susie Wolff, wife of shareholder and new Mercedes team executive director Toto, is the development driver and was first to drive the new car in a shakedown at the Idiada track in Spain before Maldonado took over for the second pre-season test starting on Tuesday.
Williams said more than 80% of the car is new, including the gearbox and rear suspension as well as radiators, floor, exhausts, bodywork and nose.
The Renault-powered team say a "considerable" amount of weight has been saved.
Reliability work over the winter had been promising, with the gearbox alone completing 3,200km on the dyno at the factory.
"This season we must be even more competitive which I believe is possible," said Maldonado, who got married over the winter break and also has a new race engineer.
"My goal is to help take the team back to the top."
The season starts in Australia on 17 March.