PITTSBURGH — Pittsburgh Steelers coach Mike Tomlin called the decision to sign James Harrison “simple and easy.”

Figuring out how — and just as important when — to use the five-time Pro Bowl linebacker, well, that part is a little trickier.

The Steelers brought the 36-year-old Harrison out of retirement on Tuesday to give an injury depleted group some needed depth and a locker room in need of some intensity an added jolt.

Harrison, who seemed to end his 12-year NFL career during an impromptu news conference Sept. 5, will provide plenty of both. How quickly he sees the field, however, remains uncertain.

“We need to see what he is capable of doing before we etch out any roles for him or others,” Tomlin said Tuesday.

The Steelers (2-1) reached out to Harrison after young linebackers Jarvis Jones and Ryan Shazier went down in Sunday night’s 37-19 win at Carolina. Jones underwent surgery Tuesday for a broken wrist.

The team placed their first-round pick in the 2013 draft on the injured reserve/return list, meaning he’ll be eligible to come back in eight weeks. Shazier’s sprained right knee likely won’t keep him out as long, though Tomlin ruled out the rookie for this Sunday.

Sean Spence will likely take over for Shazier. While Arthur Moats played well filling in for Jones — recording a sack in the second half as the Steelers pulled away — the injuries left the Steelers thin at the position.