Gerard Warren in action for the Patriots last year.
The Patriots felt the need to make a roster move with defensive linemen Mike Wright (concussion) and Myron Pryor (groin) injured. Wright led the Patriots in sacks last season (5.5) and Pryor was excellent in an interior penetrating role in the 2011 season opener against Miami (link here). But Pryor's injury status was highlighted in this week's defensive snap counts after he played just seven snaps Sunday against the Chargers (leaving the game after being stood up on a pass rush).
When comparing Gerard Warren and Landon Cohen, they have different skill sets.
Warren is 6-foot-4, 330 pounds and is more versatile in the Patriots' scheme, an option at end or tackle. He isn't an explosive interior rusher, but showed in the preseason he could still be effective in spurts.
Meanwhile, Cohen (6-3, 300) is more of a pure penetrator. His first few years in the NFL were spent with the Lions in Rod Marinelli's "Tampa-2" defense, and that type of pure up-field style is what the Patriots must have been looking for with Wright and Pryor down, as that's what they do best. Pryor and Wright are behind Vince Wilfork and Albert Haynesworth on the defensive depth chart at interior defensive line in the 4-3 alignment.
Cohen joined the Patriots late last season and was with them in training camp (football journey here).