While war was being waged on Earth against the Robotech Masters,  another war was being fought on the otherside of the galaxy.  The SDF-3  was built with the intention of folding to Tirol and negotiating for  peace with the Robotech Masters to prevent another war.  Years went into  the project and with the aid of Breetai, the SDF-3 was built using  Breetai's flagship from the first Robotech war.  The plan was simple, use  the SDF-3 as a Trojan Horse, that is make the Robotech Masters believe  that the Zentraedi are finally returning from Earth.  After they have a  foot in the door, the Robotech Expeditionary Force (REF) would be able to  open negotiations with the Masters.

The entire mission became a disastor.  The SDF-3 emerged from it's  space-fold right into the middle of an Invid force.  While the Robotech  Masters are traveling to Earth to reclaim the protoculture matrix, the  Invid have been busy laying siege to Tirol in an attempt to locate the  Matrix for themselves.  REF forces under the command of General T.R.  Edwards open up on the Invid and the REF is forced into battle with the  Invid.  Though the Ivid are defeated, they manage to cripple the SDF-3  and strand it on the far side of the galaxy.

In the same corner of the galaxy, a group of freedom fighters have been  attempting to bring down the Invid.  This group is known as the Sentinels  and they manage to forge an alliance with certain factions of the REF.   Together the REF and the Sentinels manage to defeat the Invid, repair the  SDF-3 and fold back to Earth, but not before the Invid Regiss learns of  the location of the Protoculture Matrix and takes her forces to Earth...

The Sentinels was never completly finished by Harmony Gold due to budget  problems.  Thankfully however, others took up the mantle to see that the  story of the Sentinels reached the public.  Jack McKinney retold the  series in book form.  Eternity comics, Acadamey comics, and now Antarctic  Press are in the process of translating the story into comic book  format.  The series has been running for several years and the series  should end in another couple