BOSTON -- At the start of the offseason, the goal of Red Sox general manager Ben Cherington and manager John Farrell focused on improving and adding depth to the roster.

Throughout the winter, the club has achieved that and again added to its depth Wednesday by acquiring closer Joel Hanrahan from the Pittsburgh Pirates as part of a six-player trade.

Farrell already has decided Hanrahan will be the team's closer heading into spring training, and Andrew Bailey, who was the incumbent closer but had last season cut short by injury, will serve as a late-inning setup man.

"I can't say that we went in specifically looking to upgrade or change the closer situation," Farrell said. "But as this offseason evolved, acquiring Hanrahan was a chance to do just that, and that's to improve the overall team and to add a guy with his performance history."

Farrell spoke with both Hanrahan and Bailey about their respective roles as the club prepares for spring training.

"We see Andrew as playing a very important role at the back end of our bullpen as well," Red Sox assistant GM Brian O'Halloran said. "There will be plenty of opportunities for him to help us win games in key situations late in the game and we know he's very capable of both closing and pitching in other leverage situations at the end of games. But it's not too often you get a chance to add a two-time All-Star closer to the mix, so we're excited to do that with Joel and we think it will strengthen the group and make everybody better out there."

Even before the trade was complete, Farrell informed Bailey of the team's intentions in regards to Hanrahan.

"We wanted to make sure we were out front of it a little bit," Farrell said. "We wanted to make him aware he heard from us first on this. As this deal was starting to come to a head, I just let him know what our intent was and our approach in the offseason, and that was to improve the team however we could.

"Andrew will pitch in critical moments and critical spots late in the game. I think Joel, having been a two-time All-Star as a closer the last two years, and Andrew has had success in his own right, this just bolsters the strength of our team even more so."

There are still more than six weeks before pitchers and catchers report to Fort Myers, Fla., for spring training, but Farrell likes how his bullpen is shaping up.

With the additions of Hanrahan and Koji Uehara, having a healthy and productive Daniel Bard, along with Bailey, Alfredo Aceves, Junichi Tazawa and left-handers Craig Breslow and Andrew Miller, Boston's bullpen looks solid.

"If all those guys pitch to their capabilities and remain healthy, once we enter spring training and the start of the season, the roles will become more defined," Farrell said. "But on days when certain guys might need a little bit of a rest, we've got depth and options that have closed out games in the past, and we feel like the group will benefit from one another.

"The depth and the quality of the relieving group that we have in place doesn't take away from our need to continue to get Daniel Bard back to the level he's pitched previous, but when you think of him in the group, with the addition of Uehara, and the continued emergence of Junichi, and then the left-handed complement of Miller and Breslow, this is a very strong group."