Ireland "have not played a game as physical" as Saturday's crucial Six Nations encounter at Twickenham "for a long time", says England's Eddie Jones.
Both sides seek victory to give themselves any hope of taking the title from Grand Slam-chasing France.
Jones cited the fact that Ireland have not faced the up-front force of South Africa since 2017, with England beating the world champions in November.
"Ireland know it's going to be a physical game," Jones told BBC Sport.
Such is the talent of both packs involved on Saturday, 10 of the 16 starting players have been on British and Irish Lions tours.
England prop Kyle Sinckler is one of those and, alongside Ellis Genge, he will face experienced duo Cian Healy and Tadhg Furlong in the front row.
Lions team-mates Maro Itoje and Tadhg Beirne go head-to-head in the second row, with Peter O'Mahony retaining his place in Ireland's back row opposite England captain Courtney Lawes.
Jones believes his forwards have the edge and has backed his side to "bring a physicality Ireland are not used to" adding: "They haven't played a game as physical as this for a long time."
'Biggest game' for England's young stars
The England head coach has kept faith with talented youth in the backs as scrum-half Harry Randall once more starts ahead of Ben Youngs.
Randall will partner tournament top-scorer Marcus Smith and Freddie Steward keeps the starting 15 shirt.
Jones said the must-win encounter "is the biggest game" his young stars have played in so far, adding that Ireland "will be going at Marcus".
Despite plenty of talk about England's new attack during the Six Nations, the side struggled to find any fluency against Wales last time out and eventually had to hold on for victory as their visitors fought back.
Jones defended his side, saying: "It's not a linear progression. There are little ups and downs. Particularly when you have got a young team like ours - a young nine, 10 and 15.
"It will be a test for them and we'll learn a lot. Every game they play they are learning more how to cope with the ebbs and flows of the game."
'We can disrupt Ireland'
As he has done with previous opponents, Jones has emphasised that Ireland are favourites to win at Twickenham and branded them "the most cohesive side in the world".
Jones says his side must "upset" Ireland's rhythm if they are going to win and give themselves a chance to take the title in Paris on the final weekend.
"We've worked really hard to try to find a way to do that to Ireland," he added.
"It's not easy because they are a good team but we feel we can disrupt their pattern and tempo. When you do that you create opportunities.
"The downside of being such a cohesive team is that the players rely on those patterns a lot. When the pattern breaks they start looking at each other to work out what's going on. We'll see on Saturday."