US Grand Prix: Ferrari's Vettel and Raikkonen get engine penalties

It is understood Ferrari always planned to introduce a new engine for Austin as it will allow the Scuderia fresh engines for the remaining four races while working on development for its 2016 power unit as it bids to catch rival Mercedes.

As Vettel and Raikkonen have both used up their allocation of four engines this season, following an update at Monza last month, they will incur a penalty for taking the fifth.

"We will have the hit of 10 places penalty for a new engine at this event, but it has always been the plan," said Vettel.

"It's not a big secret, no surprise for us.

"The story is that this was always the plan for us to have the strongest engine available at every single point of the season.

"I think our engine guys have done a massive job, so this should not be understood as a downside. If anything this is very positive."

The decision over whether or not to take the new engine was complicated by the fact Vettel is still mathematically in with a chance of winning this year's drivers' championship.

The German is second in the standings, behind championship leader Lewis Hamilton, but is 66 points adrift with a maximum of 100 remaining.

But Vettel said the priority is improving the power unit, rather than focusing on his slim title chance.

"If you look at just this race isolated, it's not great news, but you have to look at the whole project, the whole season, and it was always the plan to have a fresh engine here until the end of the season," he added.

"The priority was always to have maximum power at every single race.

"That has been our plan and I think it worked very well so far.

"Obviously we have to take the hit here but we should take the positive which is that we were able to make big steps, rather than just [look at] the penalty."