King James Version
And it came to pass, when Joab observed the city, that he assigned Uriah unto a place where he knew that valiant men were.English Standard Version
And as Joab was besieging the city, he assigned Uriah to the place where he knew there were valiant men.New International Version
So while Joab had the city under siege, he put Uriah at a place where he knew the strongest defenders were.