NOTRE DAME — Ethan Johnson won’t sugarcoat Navy’s option offense for the freshmen.

“You can’t really prepare for it,” he said. “Your first drive is usually your worst drive.”

The Notre Dame senior defensive end remembers his first snaps against an option offense, carefully detailing it as getting his “bottom knocked down, if you will.”

With fellow defensive end Kapron Lewis-Moore sidelined for the season with a dislocated MCL and Johnson still recovering from an ankle injury dating back to the Purdue game, the weight of stopping the Navy’s third-ranked rush attack falls largely on the shoulders of freshmen Stephon Tuitt and Aaron Lynch.

Up until recently, Tuitt and Lynch were luxury accessories to a stacked Irish defense, subbing in to give the veteran duo of Johnson and Lewis-Moore some rest. Now they’re necessities.

Saturday’s meeting with Navy will hardly be the freshmen’s first time at the rodeo, Lynch having started against Air Force and USC and Tuitt seeing significant playing time, but linebacker Dan Fox said there’s a difference between Air Force’s option and Navy’s.

“(Navy) doesn’t really come out with too many formations, they just do a lot of different things out of those formations,” Fox said. “Air Force was kind of doing a bunch of different things, running pro sometimes and this and that, and Navy kind of just does what they do and they do a good job at it.”

“It’s something you can’t really prepare for, it’s just the speed of the game,” Johnson said. “All the offensive linemen are as quick as some linebackers on Navy’s team.”

Throw in sophomore nose guard Louis Nix, who has been starting over the injured Sean Cwynar, and Notre Dame will debut a completely green defensive line on Saturday.

“The young guys are playing roles they really shouldn’t have to be playing right now,” defensive coordinator Bob Diaco said. “They’re really not ready to play the amount of reps they’ve been having to play each week.”

As for getting them ready for Navy running back Alexander Teich, who ran 210 yards on the Irish last year, Diaco said the coaching staff is doing what it can with the NCAA-regulated 20 hours of practice per week.

“They’re locked in and they’re preparing hard and the coaches are working on being as creative as we possibly can to maximize every permissible second in the allotted time that we’re allowed with them,” Daico said. “And they’ll be ready.”

And if the trio needs an endorsement, they need look no further than linebacker Darius Fleming.

“They’re working,” he said. “They’re out there every day in practice showing great attitude. They want to learn how to do it. It’s going to be a struggle because it’s different. It’s going to be tough for them now but later in the week they’ll get a hang of it and really perform.”