The SDF-7 was a flagship that Colonel Jonathan Wolfe used to save the Sentinels from the destruction of Praxis. Afterwards the group became renegades. The ship was of the Horizon-T class. (Robotech II: The Sentinels Book 3 9: Into the Fire!)
Behind the scenes
SDF-7 was a designation used in the Robotech II: The Sentinels novels to identify the new vessel used by the Sentinels after the destruction of the Farrago. Additional ships of the same class were constructed, and were referred to as SDF-7-class ships. One such SDF-7-class ship named in the novels was the Ark Angel (not to be confused the Angel class ship named the Ark Angel that appears in The Shadow Chronicles). This ship was the one used to rescue the Sentinels from the doomed planet of Praxis. The ship was then used as the Sentinel's flagship for the rest of The Sentinels' novels. Since the reboot of the series with Robotech: The Shadow Chronicles and the Prelude to the Shadow Chronicles comics/graphic novel, this designation has become obsolete.
Production model images available on DVD releases identify the Horizon-T-class shuttle as the SDF-7. This is the base model used in the Sentinels comics, with some variation. The same model sheets identify other ship-of-the-line classes as SDFs as well, and is only used as a generic name.
The SDF-7 was also referenced in Robotech II: The Sentinels Halloween Special 1.
The SDF-7 was part of the universe before the 2001 franchise reboot, thus it may no longer be in continuity.