As training camps open, several units are barely recognizable from the 2013 season — whatever the reason. Here are the five NFL defenses that look the most different from last year.

Dallas Cowboys

What’s new: Defensive end DeMarcus Ware was released; linebacker Sean Lee tore his ACL and is out for the season; defensive tackle Jason Hatcher left as a free agent to Washington; defensive tackle Henry Melton signed as a free agent from Chicago; drafted seven defensive players including defensive end Demarcus Lawrence and linebacker Anthony Hitchens.

For better or worse? Worse, which is a problem since they gave up the most yards in the NFL last season. Ware, no matter how injured he was last year, is difficult to replace. Lee is practically impossible.

Denver Broncos

What’s new: Defensive end DeMarcus Ware, cornerback Aqib Talib and safety T.J. Ward signed as free agents; linebacker Wesley Woodyard, cornerbacks Dominique Rodgers-Cromartie and Champ Bailey and Des Shaun Phillips and Robert Ayers left as free agents; drafted cornerback Bradley Roby in the first round.

For better or worse? Better, or at least the front office is betting millions that it is. It was an all-in offseason and an arms race with the Patriots, with the offense getting a few tweaks but the defense getting a massive infusion.

Chicago Bears

What’s new: Defensive end Julius Peppers was released; defensive tackles Henry Melton and Corey Wootton left as free agents; defensive ends Jared Allen, Lamarr Houston and Willie Young and safeties Adrian Wilson, M.D. Jennings and Ryan Mundy signed as free agents; defensive tackle Nate Collins returns from October knee surgery; defensive tackle Jeremiah (formerly Jay) Ratliff enters first full season with team; four of first five draft picks are on defense, led by first-round pick cornerback Kyle Fuller.

For better or worse? Has to be better, since last year’s defense was the worst in franchise history by almost any measure.

Arizona Cardinals

What’s new: Cornerback Antonio Cromartie and linebacker Ernie Sims signed as free agents; linebacker Karlos Dansby left as a free agent to Cleveland; cornerback Tyrann Mathieu likely will start season on PUP with knee injury; linebacker Daryl Washington serving season-long drug suspension; drafted safety Deone Bucannon in the first round.

For better or worse? Worse, by the margin of Washington’s suspension, which jarred and angered the organization. Beefing up the secondary helps, but the NFC West is not the division in which anyone can afford to step back.

Oakland Raiders

What’s new: Drafted six defensive players, led by linebacker Khalil Mack; defensive ends Justin Tuck and Antonio Smith, cornerbacks Carlos Rogers and Tarell Brown and linebacker LaMarr Woodley signed as free agents; defensive end Lamarr Houston and cornerback Tracy Porter left as free agents.

For better or worse? Better. Mack will give Jadeveon Clowney a run for best defensive player drafted this year. Tuck and the rest are a major investment, especially since the offense has a lot of catching up to do.