Williams believe they can compete at the front of the 2009 F1 grid having given their new car a low-key debut at Portugal's Portimao test track.
The FW31, still in its dark blue winter testing livery, was quietly wheeled out alongside test driver Nico Hulkenberg.
Like its 2009 rivals, the car features a wide nose and tall, narrow rear wing.
"Under-expect and over-deliver is the best way," said technical director Sam Michael. "But there is more of a level playing field than for many a year."
Williams have committed their future to Formula One following the sport's recent financial uncertainty, but know an improvement on last season's dismal eighth-place finish in the constructors' standings is vital.
The new-look wings on the FW31 are in keeping with those sported by the other cars so far unveiled - Ferrari's F60, Toyota's TF109, McLaren's MP4-24 and Renault's R29.
But the aerodynamic design appears slightly different, and Michael admitted a considerable proportion of the team's 2008 resources had been channelled into the 2009 car.
"We probably started work on this car at the same time as others, working in the wind tunnel in December 2007 and drawing many of the parts six weeks before that," said Michael.
"But the difference is, going into 2008 we increased our resource significantly throughout last season, which is why we took quite a big penalty on the old car.
"Hopefully that will pay off now with a more competitive 2009 car."
One significant difference with the Williams is that the team are testing a flywheel kinetic energy recovery system, the device that stores energy under braking.
All their rivals have chosen the alternative battery option, which Williams have also explored, but the team have yet to decide whether they will begin the season with either on the car.
There are some big differences across the cars at the moment, and that's the great thing about Formula One
Williams technical director
"The rules are so different aerodynamically, and that is really exciting," said Michael of the differences between his car and those of his rivals on the grid.
"That's why I'm in Formula One, to be honest. If you look at periods like this, from an engineering point of view it's fascinating to see people come up with different concepts.
"It's really exciting to see which ones are good and which ones are not, and there'll be a massive fever of development during the year because of that.
"There are some big differences across the cars at the moment, and that's the great thing about Formula One."
However, the FW31's first full outing ended on a flat note when Hulkenberg aquaplaned off the circuit after completing 17 laps, damaging the front nose.
Despite his wobble, Hulkenberg, who will be replaced by race driver Nico Rosberg for Tuesday's testing session, was pleased with the car's first outing.
"Straight away the new car feels OK," said the German.
2009 CAR LAUNCH DATES
20 Jan: BMW Sauber
9 Feb: Red Bull
TBC: Toro Rosso, Force India, former Honda team
"I feel comfortable in it and for a new car we've had a trouble-free morning technically.
"The important thing for today is simply to make sure we run through all the checks of the basic systems on the car and confirm everything is working as it should. So far that is the case and we can be happy."
Team boss Frank Williams added: "By the time we get to Melbourne, I would expect the usual suspects to still be dominating the top two positions.
"More importantly, I hope Williams will have made a significantly large step forward with the FW31."
Williams, who have kept drivers Nico Rosberg and Kazuki Nakajima for 2009, will not unveil their car in its full race colours until the end of February.
The FW31 will receive further enhancements ahead of its debut appearance on the grid in Melbourne, Australia, for F1's first race weekend of 2009.