Way back in the spring, Oklahoma started preparing, a little at a time, for Army's triple-option offensive attack.
They did the same thing during preseason camp, before they started opponent-specific work for any other team they'll face this season.
The No. 5 Sooners (3-0) will put that preparation to the test Saturday against the Black Knights (2-1) when the teams meet in Norman, Okla.
"It's a challenge," OU head coach Lincoln Riley said.
"It's one of those as a coach, you sit there and [think], all right, if we spend all this time preparing for them, then we're not preparing for the other however many games we play. And if we don't spend enough time, then they'll come in and beat you, and that's the reality of it.
"They're good enough to do it."
Army's triple-option attack is one that few college teams run, and one the Sooners haven't faced since 2010 when they played Air Force -- though Tulane used some option principles a year ago.
"Defending the triple-option is strictly assignment football," Oklahoma middle linebacker Kenneth Murray said. "If you don't do your assignment they can bust one for a touchdown. Everybody has to be honed in on their keys."
Murray's reads on the option -- especially against Army quarterback Kelvin Hopkins Jr. and fullback Darnell Woolfolk -- will be important. The sophomore middle linebacker has 19 tackles over the last two games and has shown improvement from a year ago when he struggled at times, especially defending the run.
The Black Knights average just 140 yards per game through the air, among the lowest in FBS. Army has attempted an average of just 13 passes per game, but it is sixth nationally in rushing at 306.7 yards per game.
Hopkins, a 5-foot-10 junior, is in his first season as the starter, replacing standout Ahmad Bradshaw. Hopkins has a team-high 206 rushing yards and has completed 18 of 38 passes for 420 yards, with two touchdowns and no interceptions.
"He's gotten better every week he's played," said Army coach Jeff Monken, whose team beat Liberty and Hawaii after dropping its opener at Duke.
"That's encouraging. It's been fun to watch -- to see him lead and grow in his confidence. I think he is a confident young man, but to see his confidence in running this offense and being a leader of this team has been a lot of fun this week. And I hope he can continue to get better."
Oklahoma's new starting quarterback, Kyler Murray, has quickly established himself as a Heisman favorite as he steps into the shoes of 2017 Heisman winner Baker Mayfield.
Murray is a flurry of activity at 5-foot-10, last week passing for a career-high 348 yards and three touchdowns, also rushing for 77 yards in a 37-27 win at Iowa State.
He ranks fifth nationally in yards per pass attempt (11.8), sixth in yards per completion (17.6), sixth in passing efficiency (199.8) and 11th in total offense (344.0 yards per game). Wide receiver Marquise Brown, whose big plays this season include touchdown catches of 75, 65 and 58 yards, has the kind of speed that Army rarely sees.
"Oklahoma is an unbelievable football team," Monken said.
"They are talented, well coached and very difficult to beat. They're really good. It's going to be a tremendous challenge for us. ... They've got several Parade All-Americans, and as (former Navy and current Georgia Tech coach) Paul Johnson used to say, we have several guys who have marched in a parade."
Oklahoma did lose running back Rodney Anderson to a season-ending knee injury, with sophomore Trey Sermon now the clear No. 1. Sermon rushed 13 times for 74 yards and a touchdown against Iowa State.
"I think a little bit is just seeing how he handles the whole deal, which he did a great job of in the first game against Iowa State," Riley said. "He's really close to breaking loose and making even a few more explosive plays as well. He's definitely one right now, but we're going to need more."
These teams haven't met since 1961, with Oklahoma holding a 2-1 edge in the series. Saturday's game marks the beginning of a home-and-home series, with the Sooners set to travel to West Point, N.Y., on Sept. 26, 2020.