Complete the Proving Grounds strike aboard the Halphas Electus.
Vanguard High Command has issued a challenge to the new Cabal Empire. A Vanguard victory will drive the Cabal from the Sol system, whereas a defeat would see the City brought under Cabal control. It falls to you. Defeat Caiatl's Champion aboard the Imperial Land Tank, Halphas Electus, and show them that Guardians do not bow to outside aggressors.