They've beefed up their pass coverage with the additions of cornerbacks Nnamdi Asomugha and Dominique Rodgers-Cromartie. And they upgraded their pass rush by signing end Jason Babin and tackle Cullen Jenkins, who combined for 19 1/2 sacks last season.
But sandwiched between their improved defensive line and their all-world collection of corners is a linebacking corps that, in the coming weeks and months, needs to prove it isn't the weak link that's going to bring this defense down.
"I know people have some doubts about us, but I think we're going to be ready," said Moise Fokou, the team's starting weakside linebacker heading into tomorrow's first preseason game against the Baltimore Ravens. "We're going to be all right."
He may very well be right. But at the moment, there still are questions about his unit, if only because it's so unproven.
The three players currently at the top of the depth chart - Fokou, second-year strongside linebacker Jamar Chaney and rookie middle linebacker Casey Matthews - have a grand total of 3 years of NFL experience. Collectively, they've got just 19 NFL starts, none at the positions they currently are playing.
Fokou, a seventh-round pick in the 2009 draft, spent most of last season on the other side, as the team's starting strongside linebacker. Chaney, a seventh-rounder in last year's draft, started three late-season games at middle linebacker, including the Eagles' playoff loss to Green Bay, after Stewart Bradley dislocated an elbow.
Matthews, a fourth-round pick in the April draft, has been taking the first-team reps in the middle since the first practice of training camp. While it's possible new defensive coordinator Juan Castillo just wants to give him as many reps as possible early on so that he can learn the defense, it appears that the plan right now is for him to be the season-opening starter at the MIKE position.
"Casey's really done a great job of handling the huddle," Castillo said. "He's got poise, composure. Sometimes I'll mess up a word here and there. But he's able to put things together. He does a good job."
While Matthews has passed his early camp test, what ultimately will decide whether he remains at the top of the depth chart is how he plays in the Eagles' four preseason games when you have to actually tackle somebody.
"Coach [Andy] Reid will tell you that's what camp is for," Castillo said. "For competition. Those guys will get the first opportunity. The other guys, we'll look at tape and grade them. And then we'll take it from there."
Of the nine linebackers the Eagles have in camp, just two were drafted higher than the sixth round, Matthews and 2010 fourth-rounder Keenan Clayton. Four of the nine are rookies and two are second-year players. A seventh, Rashad Jeanty, who was signed off the street last February, hasn't played in an NFL game since the '09 season.
Aside from Jeanty, who has 32 career starts, their most experienced linebacker is Akeem Jordan, a fifth-year player who was the season-opening starting SAM last year before getting benched in favor of Fokou in Week 5. Aside from quarterback Michael Vick, who the Eagles franchised, Jordan was the only one of 15 unrestricted free agents from last year's team who the Birds bothered to re-sign.
Castillo said he isn't concerned about the lack of pedigree at linebacker. Or the lack of experience.
"When you look at players, [defensive end] Trent Cole was a fifth-round pick and he's a very good player," he said. "[Cornerback] Asante Samuel was a fourth-round pick. I don't think you have to go out and get [proven] free agents for them to be players.
"We feel real good about our young kids. They're going to have to develop. But right now, they're progressing well. We're going to see where we are on Thursday. But then we still have [time]. It's a process. Any time you get a young kid, it's a process. But they have to keep getting better."
If Castillo ultimately decides that Matthews isn't ready to start, the likely fallback plan would be to slide Chaney back inside. Right now, though, Chaney and Fokou both are playing totally new positions.
Chaney played WILL his first 2 years at Mississippi State and MIKE his last 2. Spent his rookie season with the Eagles as a MIKE. He's never played SAM.
"It's different from the MIKE," he said. "But we've got great teachers here and the transition has gone pretty well. I feel like I'm playing faster right now."
Fokou was a SAM at the University of Maryland, and has played MIKE and SAM since being drafted by the Eagles. He's never played WILL except in training camp as a rookie when he got a taste of all three linebacker spots.
Castillo insists it's no big deal what side Fokou and Chaney play on.
"Really, the way we play it, [the linebackers] don't play on the line," he said. "So they're interchangeable. For [Fokou], when he was a SAM and the tight end was flexed [out], it's no different than where he lines up now and there's a receiver that's flexed. Everybody has different gap responsibilities depending on the formation or on the front call."
That's true to a degree. But the fact of the matter is, your SAM usually needs to be a bigger guy who can slow down the tight end when he heads into his route, and who can take on blocks in the run game and funnel the play back inside.
The WILL usually needs to be your fastest linebacker since he plays in space and often has to cover running backs coming out of the backfield and stay with receivers on crossing patterns.
Fokou isn't slow, but he's more suited to play SAM. In fact, last year, general manager Howie Roseman said one of the reasons the Eagles drafted him 2 years ago was because of his experience at Maryland as a SAM.
"I feel comfortable out there," Fokou said. "It helps that when I came in my rookie year, the coaches allowed me to play all three positions. So I kind of got a chance to see how all three positions are played. This being my third year and understanding defenses more so this year, it's allowed me to come in and pick it up pretty quickly."
If things don't go well in the preseason, Castillo has some options. As previously mentioned, Chaney can move back into the middle if Matthews struggles. If Fokou turns out to be a little too slow to play WILL, the coaching staff is very high on speedy second-year man Clayton, who played well in a limited role in nickel late last season. And Jordan can play all three linebacker spots.
"We're pretty happy with the results right now and the way everybody's picking things up," Fokou said. "I think we're going to be ready. We're going to be all right."