Compton to be first new face in January.
The 24-year-old has played twelve times in League One for Portsmouth but was on a short term deal with the south coast club.
And Joe has moved quickly to sign the pacey left winger on a permanent contract, with the deal set to come into force from January 1st.
Jack started out at West Brom and enjoyed a number of loan spells away from The Hawthorns, including time with Phil Parkinson at Bradford City last season.
A summer move to Pompey followed and Jack played against the U's at the Weston Homes Community Stadium earlier this season, playing 84 minutes.
Jack's move will be completed subject to relevant paperwork clearance from the footballing authorities.
Summer Brochure Final Edition