Historically, the Pittsburgh Steelers are known for their defense.

When the Steelers faced the Seahawks in Super Bowl XL, Ben Roethlisberger was a second-year quarterback who benefitted from having the league's third-best defense. When the Steelers returned to the Super Bowl in 2008, Roethlisberger had established himself as one of the NFL's best young quarterbacks. But the defense had also improved -- to the No. 1 unit in the league and arguably one of the most complete defenses of the last decade. Similar story in 2010, Pittsburgh's last Super Bowl appearance; Roethlisberger carried the offense, but a dominant defense (again ranked No. 1) was that team's hallmark.

But things began to change in 2011. The D ranked seventh, according to Football Outsiders, but a wild-card playoff loss to Tim Tebow and the Broncos ended their season on one improbable 80-yard scoring play.

By 2012, the defense dropped to 13th before falling to 19th in 2013 The Steelers went 8-8 both seasons. Pittsburgh returned to the postseason in 2014, but it was due in large part to one of the league's most explosive offenses. Led by Roethlisberger, Antonio Brown and Le'Veon Bell, that group ranked second behind only Aaron Rodgers and the Packers. Meanwhile, the defense continued to languish, falling to 30th. In more sobering terms, they were third from the bottom ahead of only the Falcons and Saints.

We talked about the Steelers' chances in 2015 on the latest Eye on Football Podcast (remember to subscribe via iTunes):

If the old saying that defense wins championships still holds, it now comes with some caveats. High-powered offenses are more regularly carrying inept defenses. And for as high-powered as the 2014 Steelers' offense was, the reality is that this team hasn't won a playoff game since the 2010 season. If that's going to change in 2015, Big Ben & Co. are going to have to be even more explosive -- or the defense will need to get better.

The good news is that the defense, now run by Keith Butler, doesn't have to return to its 2008 glory, it just has to be average, if that.

So what does that mean, exactly? Looking at Football Outsiders data from 2008-2014, there are plenty of instances of very good offenses carrying average-or-worse defenses into the playoffs. The most glaring example is the 2011 Patriots, who went 13-3, featured a top-ranked offense to go along with the 30th-ranked defense, and were eventually stymied in the Super Bowl by arch nemesis Eli Manning and the Giants.

The team most like the '14 Steelers? The '14 Packers. Green Bay had the only offense more efficient that Pittsburgh's last season, according to FO's metrics, but the difference was its defense was a definition-of-mediocre 16th. And while the Packers ended up losing to the Seahawks in the conference championship game, that had almost everything to do with terrible luck and even worse play-calling from coach Mike McCarthy.

TEXTHERE. (CBSSports.com, via Football Outsiders)
 (CBSSports.com, via Football Outsiders)

Of course, none of this guarantees a Lombardi Trophy. To paraphrase A's general manager Billy Beane: "Sh-t doesn't work in the playoffs ... What happens after that is f--king luck." Beane was talking about the Moneyball philosophy of building a roster but the underlying truth holds here: In the one-and-done playoff format, anything can happen (ask the 2014 Packers, or any Patriots' teams that had to face the Giants).

But the idea of a great offense coupled with a middling defense seems like a reasonable starting point for success in the salary-cap era, where resources are scarce and have to be allocated with precision.

That brings us back to Pittsburgh, where there is one big asterisk to all this talk of improving defenses: The offense has to be just as good as it was last season. That means Roethlisberger throws for nearly 5,000 yards, Brown hauls in close to 130 passes for some 1,700 yards, and Bell has some 2,500 all-purpose yards. The production doesn't rest solely with these three players -- this could be Martavis Bryant's breakout season and Markus Wheaton continues to get better -- but it's where the conversation begins.

The conversation continues on the other side of the ball. The Steelers used three of their first four 2015 draft picks to improve a bottom-of-the-barrel defense, starting with rush linebacker Bud Dupree, taken 22nd overall. Cornerbacks Senquez Golson and Doran Grant were added in Rounds 2 and 4. It's a familiar theme: Pittsburgh drafted linebacker Ryan Shazier and defensive end Stephon Tuitt in Rounds 1 and 2 in 2014, and outside linebacker Jarvis Jones was the 17th overall pick in 2013.

But the infusion of youth, which coincides with the departures of Troy Polamalu, Ike Taylor and Brett Keisel -- important pieces in the defense's long run of dominance -- also comes with growing pains. It explains the lackluster sack totals and everything that follows -- the struggles in pass coverage, and even issues stopping the run.

“I tell [the Steelers' young linebackers], ‘You could put all your sacks together and you won’t have as many as me so you’re going to listen to me," said outside linebackers coach Joey Porter, who had 98 career sacks during 13 NFL seasons. "You can put all your sacks together and I’d still have more than you, so why wouldn’t you listen to me when I’m trying to tell you how to get to the quarterback?"

Dupree, the rookie out of Kentucky, seems all in.

"I want to be in that group that brings it back," he said last week, via Cleveland.com. "We want to bring back that hunger, that eagerness to go after the quarterback."

It sounds good a month out from training camp, but what it means once the pads are on and grown men are running full speed into each other is another matter. Of course, Dupree and the rest of the 20-somethings won't have to do it alone. There's James Harrison, who is impervious age, heat, left tackles and God knows what else.

Field temp 189.5, temp 6ft above the field 136...... Grooving on Sunday Arizona heat

A video posted by James Harrison (@jhharrison92) onJun 28, 2015 at 2:18pm PDT

Will it be enough? We'll know one way or the other in the coming months.

Can James Harrison and Bud Dupree return the Steelers' D to its glory days? (USATSI)
Can James Harrison and Bud Dupree return the Steelers' D to its glory days? (USATSI)