Williams believe they have made "significant progress" after revealing their car for the 2018 Formula One season, while Robert Kubica announced his schedule at the car's launch.

Kubica will play a part in an F1 campaign for the first time since suffering life-altering injuries in a rally crash and the Pole is set to feature in three practice sessions this year.

He had been tested for a seat at Williams and Renault, but was not considered by the French squad, while Sergey Sirotkin was preferred in the race seat for the Grove-based outfit.

Sirotkin will make his debut alongside Lance Stroll, the Canadian teenager whose own introduction to the sport was mixed in 2017. Stroll secured a podium finish in Baku, the only driver outside of Mercedes, Ferrari and Red Bull to do so last year, but also struggled routinely in qualifying and was a way off team-mate Felipe Massa in the standings.

Williams' 2018 challenger features notable changes to its aerodynamic parts, the team attributing a new look to the influences of former Mercedes technical chief Paddy Lowe and former Ferrari aerodynamicist Dirk de Beer, who joined the team during the previous season.

Lowe said in a statement: "The car has many new features, most of which are not all that obvious, but externally the team has pursued a very different aerodynamic concept which has allowed us some significant progress in aerodynamic performance.

"All Formula One cars are an evolution of what has gone before to some extent, but the FW41 does involve a number of departures from the directions that have been pursued in the past. Overall, the philosophy we are starting to see emerge is a new approach to the collaboration between aerodynamics and design to achieve the optimum working result."

Williams finished fifth in the constructors' standings last term, albeit 104 points adrift of fourth-place Force India.