Williams will have a picture of Ayrton Senna on their car this season as Formula One marks the 20th anniversary of the triple champion's death.
Williams provided a first glimpse of their new Formula One car with a confident prediction that it would be good enough to move the former champions back up the grid after a dire 2013 campaign.
Brazilian Felipe Massa put Williams on top on the penultimate day of pre-season testing in Bahrain on Saturday while Red Bull's quadruple world champion Sebastian Vettel failed to complete a lap.
Finland's Valtteri Bottas and Brazilian Felipe Massa will stay at Williams in 2015 after the resurgent Formula One team announced on Sunday what had to be one of their easiest decisions of the season.