Montgomery on Friday announced the signings of quarterback Thomas Sirk, running back Tyshon Dye of Clemson and defensive lineman Gaelin Elmore of Minnesota. All can play immediately and have one year of eligibility remaining.
Sirk was the quarterback when Montgomery was the Blue Devils' offensive coordinator in 2015. Sirk missed last season after injuring his Achilles tendon twice in seven months, but he threw for 2,692 yards and 19 touchdowns and rushed for 16 TDs in 24 career games at Duke.
He announced in April that he was planning to play for the Pirates in 2017.
The Pirates went 3-9 last season, and Sirk should have a legitimate chance to win the starting quarterback job.
Dye was a backup for the Tigers' national championship team last season. Elmore started six games last season for the Golden Gophers.
Information from ESPN's Andrea Adelson and The Associated Press contributed to this report.