One of the biggest surprises of the 2014 NFL season was the improvement of the Dallas Cowboys defense in the first year under coordinator Rod Marinelli. Now, one month into the offseason, it looks like that group could be even better in 2015.

The Cowboys took a big step toward that end this week by retaining middle linebacker Rolando McClain on a one-year deal. McClain, the twice-retired former first round pick, was a breakout star in his first season with Dallas last year.

After middle linebacker Sean Lee went down with an ACL tear on the first day of OTA, the Cowboys acquired the rights to McClain, who sat out the entire 2013 season, from the Baltimore Ravens along with a seventh round pick in the 2015 draft for a 2015 sixth round pick. It was a low-risk move for Dallas that ended up paying off like a winning lottery ticket.

Not only did McCain come out of retirement to play for Dallas, he finally found his motivation to play the game under Marinelli and Cowboys head coach Jason Garrett, and filled the sizable void left in the middle of the Dallas defense with the injury to Lee. McClain played in 13 games for Dallas in 2014, including 12 starts and finished with 87 tackles, a sack, a forced fumble, three pass defensed and two interceptions.

Having McClain in the middle of the defense was a game-changer for the Cowboys and a big reason they ticked up from the last-ranked defense in 2013 to middle of the pack in 2014. The Dallas offense had a lot to do with that as well, as their run-heavy, clock-control style kept the defense off the field. Only two defenses spent less time per game on the field than the Cowboys last season: the Pittsburgh Steelers and the Seattle Seahawks.

For the Dallas defense to build on that success next season, they’ll certainly have to find a way to create similar offensive production despite the departure of the NFL’s leading rusher DeMarco Murray. But retaining McClain helps there too. His presence allows the Cowboys to take a different draft approach and target the best player available instead of reaching to fill a need a linebacker. That could potentially allow Dallas to take Murray’s replacement early in the draft where the talent is premium, making for a seamless transition, which would in-turn put the defense in a better position to succeed.

Though the offense — and the success of the running game — played a big role in the Cowboys’ defensive revival in 2014, and likely will again in 2015, it can’t be understated how the growth of Dallas’ personnel on that end helped execute the team’s turnaround on defense.

McClain was one of several players to step up last season. Defensive end Jeremy Mincey was an excellent contributor after signing a cheap two-year deal last March. The Cowboys also got solid late-season contributions from second round pick Demarcus Lawrence after he completed a slow recovery from a fractured foot.

In addition to McClain, the Cowboys were buoyed by the play of their other linebackers as well. Rookie fourth round pick Anthony Hitchens emerged as a jack of all trades, playing all 16 games, including 11 starts, while occupying all three linebacker spots at one time or another. Veteran Justin Durant got off to an excellent start before a torn biceps in Week 6 ended his season. In stepped Bruce Carter and the fourth-year pro had one of his best seasons, finishing with 82 tackles, 11 passes defensed and five interceptions.

McClain, Durant and Carter were all free agents this offseason and Dallas’ ideal scenario would have been to keep two of them to ensure depth. However Carter quickly priced himself out of those plans and eventually signed a four-year, $17 million deal with the Tampa Bay Buccaneers. Durant also went elsewhere, signing a three-year, $10.8 million deal with the Atlanta Falcons.

The Cowboys added some depth by signing former Charger Andrew Gachkar and former Viking Jasper Brinkley, but neither projected as a starter. Up until this week Dallas was locked in a high-stakes standoff with McClain. Few teams were bidding on the Dallas reclamation project, wary of his flaky history of wavering passion for the game, as well as the impending four-game fine he is facing for a violation of the league’s substance abuse policy. That penalty leaves him just one transgression away from a suspension.

But after the New England Patriots finally brought McClain in for a visit, the Cowboys blinked and agreed to terms with the linebacker on an incentive-laden one-year contract. But the incentives mean that McClain will have to stay on the field to earn all of the potential $3 million in the contract. Provided he does stay on the field, having McClain back in the fold at middle linebacker is an important step toward completing the defense.

Now McClain can be penciled into the Mike linebacker spot and the returning Lee is expected to occupy the Will. Hitchens is currently set as the Sam, but that’s one of many options the Cowboys have there. They could still look to pick a strong side backer early in the draft if the right guy comes their way, and shift Hitchens back into the depth role he thrived in last season. Dallas is as deep at the position as they have been in years with Brinkley, Gachkar, a special teams ace, and Kyle Wilber currently set as the second teamers. One more strong addition to that group via the draft would make it a core strength of the Dallas defense.

The Cowboys defense can also be projected to be stronger up front next season, through both growth of the players in place and personnel additions. The headline move is the signing of Greg Hardy, who had established himself as one of the league’s best pass rushers with 26 sacks between the 2012 and 2013 seasons, before last season when his involvement in a domestic violence case shelved Hardy for all but one game of the campaign.

That case continues to hang over Hardy, with a suspension for part of the 2015 season likely to come down in the next few weeks after the NFL completes its investigation. Whether that suspension is merely 4-6 games or as many as 12, as some have speculated it might be, could force the Cowboys to adjust their plans. But they’ve mitigated their risk somewhat by loading Hardy’s contact with incentives, ensuring that they won’t be paying him unless he’s playing for them.

For however long he’s out, the Cowboys will rely on the two aforementioned players that emerged to lead the defensive line group last season: ends Mincey and Lawrence. Mincey was an impressive find by the Dallas front office. The seven-year pro had flashed potential during his time with the Jacksonville Jaguars, but had a weak 2013 season. After playing in just eight of Jacksonville’s 13 games, he was released and wound up in Denver, where he did participate in all three games of Denver’s Super Bowl run, but made limited contributions.

After the departure of DeMarcus Ware from Dallas to Denver, the Cowboys inked Mincey to a reasonable two-year deal as a depth signing, but myriad injuries pressed him into a starting role early and he held it down for all 16 games, with six sacks, two forced fumbles, two fumble recoveries and 46 tackles. If he has to start again while Hardy is suspended, the Cowboys know now that they can count on Mincey.

On the other side, they’ll be relying on a breakout season from Lawrence regardless of Hardy’s situation. Dallas traded up to select Lawrence out of Boise State at the top of the second round last season (34th overall), with an eye on plugging one Demarcus in for another as a replacement for Ware. But Lawrence suffered a foot fracture during training camp that set back his development significantly. He didn’t get on the field until Week 9 and even then he was mostly invisible for the duration of the regular season.

However, in the postseason, Lawrence hit his stride. He came up with one of the biggest plays in the Wild Card round win over Detroit when he made up for an earlier gaffe — when he recovered and then lost a fumble — by getting to Lions quarterback Matthew Stafford, stripping him and falling on the ball to clinch the Dallas victory. One week later he was one of the few bright spots for the Cowboys defense against the Packers, and his performance included a sack of Aaron Rodgers. Lawrence’s play in the two biggest games of the season left Dallas salivating about what he could bring in year two with another offseason of development and a full training camp.

Lawrence isn’t the only Boise State product the Cowboys are counting on up front. Dallas believes they’ve found an answer to some of their interior defensive line woes in 3-technique tackle Tyrone Crawford. Crawford was selected in the third round of the 2012 draft out of Boise as a defensive end, and played all 16 games there in his rookie season. But after he suffered a torn Achilles in training camp in 2013, Crawford became more of a swing lineman while the Cowboys sought to make the most of his versatility.

They used him inside and outside in the 2014 preseason, and he started the regular season as LDE. But by the Week 4 game against New Orleans, the Cowboys had moved him inside, where he remained the rest of the season. Dallas sees Crawford as a rising star along their line, versatile enough to help against the pass and the run. Alongside Crawford for most of the season was Nick Hayden, who started all 16 games for the Cowboys in 2014. But while Hayden has been a steady starter for Dallas the last two seasons, he represents the clearest weakness along their defensive front and they’d love to find a true 1-technique in the draft to shift Hayden into a depth role.

The Cowboys already have a lot of backend depth on their defensive line with a slew of interesting prospects including Davon Coleman, Ken Bishop, Ben Gardner and Chris Whaley, all rookies last season. They also have former starter Josh Brent in reserve, as well former Texans first round pick Amobi Okoye. Okoye has spent the last two seasons recovering from Anti-NMDA receptor encephalitis, a condition of the brain, which causes memory loss and seizures. During his struggle with the disorder, Okoye was put into a medically induced coma and many believed he would never play again. But he spent all of last season working with the Cowboys and is now targeting 2015 for his true return to the NFL.

Okoye is still just 27 years old and if he can realize the potential that made him a Top 10 pick and had him start all but six games for the Texans in his first four seasons, he’ll certainly be in the mix for playing time. Dallas also recently added to their depth at defensive end by signing British prospect Efe Obada, who impressed in five games played for the London Warriors of the British American Football Association National Leagues. With all that potential on the back end of the defensive line depth chart, if the Cowboys can add one more true talent via the draft at 1-technique, they would be in great shape up front.

They’re also in pretty good shape on the back end, where Barry Church and J.J. Wilcox hold down the safety spots. Church has been one of the most steady contributors to the Dallas defense over the last two seasons and though he has his flaws — particularly in coverage against tight ends in a passing league that is trending more and more toward targets at that position — he is a solid tackler, run stopper and playmaker. Wilcox has been up and down in two seasons with the Cowboys but his presence offsets Church well. Where Church struggles, in coverage, Wilcox is stronger. Where Church is at his best, ball pursuit, Wilcox often takes poor angles and turns big plays into bigger plays. Between the two of them, Dallas has one really good safety, and while they’d probably prefer to have two really good safeties, Church and Wilcox can do a passable job for now.

The one major deficiency that remains on the Dallas defense is one they’re almost certain to try to remedy via the draft: cornerback. The Cowboys last truly attempted to fix their problems at the position in 2012 when they inked one of the top cornerbacks on the free agent market in Brandon Carr to a five-year deal and then moved up in the draft to select Morris Claiborne with the sixth overall pick. But neither of those moves has worked out as planned.

Carr has shown flashes but been a massive disappointment overall, culminating in a 2014 season where he went without an interception for the first time in his career. He did show some improvements under Marinelli in coverage as the Cowboys made some defensive tweaks to allow him to play more of his preferred man-press coverage. He also appeared to be improved as a tackler in the open field, but he was still ranked 90th among 108 qualified corners last season according to Pro Football Focus.

It remains to be seen if Carr is even on the roster come training camp. Dallas has been attempting to negotiate a restructure/pay cut with him to get some salary cap relief from his $12.7 million hit in 2015, but Carr has been resistant. If he continues to resist, the Cowboys could designate him a Post-June 1 cut and save $8 million this year and $9 million next year.

But if they decide to do that, Dallas doesn’t have a whole lot of options to replace him. Orlando Scandrick has emerged as a leader of the secondary group and one of the leaders of the defense, but he is a slot corner through and through and pressing him into duty on the outside may only serve to expose his flaws. Claiborne is coming off an ACL tear in Week 4 of last season, so it’s uncertain if he’ll be ready to start the season. Even if he is, the Cowboys can’t put much trust in him. Prior to the 2014 knee injury, Claiborne was nagged by a litany of injuries throughout the 2013 season that made him unreliable and when he did get on the field he struggled greatly in coverage.

Dallas did add former Saints cornerback Corey White, but White ranked as one of the worst defensive backs in the league last season and projects as simply a depth signing. The Cowboys like undrafted free agent Tyler Patmon, but he still has strides to make in development before he can be relied upon.

With the free agent cornerback market dry, Dallas will turn to the draft. But the lone truly elite talents at the position in this year’s draft, Trae Waynes and Marcus Peters, will likely be gone by the time the Cowboys pick in the first round. There are, however, several second tier options that could help Dallas, and that second tier is so deep, it might allow them to get a similar talent in the second round to what’s available late in the first.

Signing McClain allows them to weigh their options more carefully in that regard. Without him, the Cowboys would have been forced to target a linebacker early. Instead they can aim to draft heavy on defense while targeting the best players available and best fits at cornerback, linebacker and defensive tackle to inject their defense with youth and talent. That’s how and why retaining the man at the middle of their defense pulled together Dallas’ offseason plan.