England face Wales at Twickenham on Saturday in a crunch Group A tie that could either lift or irrevocably damage both sides' World Cup campaigns.
England coach Stuart Lancaster has made the bold call to pick union rookie Sam Burgess at inside centre, while Gatland has made nine changes to the side that destroyed Uruguay last week.
Experience is on Wales' side...
Much has been made of injuries to some of Wales' key players and the relative newbies such as Hallam Amos (three caps), Gareth Davies (four caps) and Thomas Francis (two caps) who have come into the side.
Yet on average, Wales' starting XV is more experienced:
- Average caps: England 29.4 - 42.1 Wales.
Read more: England willing to go for Burgess
Although England's team is older...
- Average age: England 26.5 - 25.9 Wales.
Wales have the height advantage...but there's not much in it.
- Average height: England 187.9cm - 188.8cm Wales.
And the power is with Wales' pack
Wales' starting scrum is almost 40kg heavier than Englands':
- Weight of scrum: England 906kg - 940kg Wales.
Stuart Lancaster has the better of Warren Gatland so far
- Head-to-head: Lancaster 2 - 1 Gatland.
In head-to-head meetings, Lancaster's England has won twice and lost twice to Wales - but Gatland was only in charge for one of those wins (the Kiwi coach put Wales duties on hold in 2013 to coach the British and Irish Lions).
Read more: Wigglesworth expects fierce Wales test
But captains Chris Robshaw and Sam Warburton are tied on victories
- Head-to-head: Robshaw 2 - 2 Warburton.
Both sides have relatively unfamiliar line-ups
According to Opta, both Wales and England have only eight players in Saturday's starting XVs who started when the two sides met in the Six Nations earlier this year.
England had George Ford and Luther Burrell playing at fly-half and inside-centre on that occasion, Owen Farrell and Sam Burgess take up the positions this weekend with Ford dropped and Burrell not even picked in the World Cup squad.