The Sixth Battle Cruiser Division is a unit within the Lost Fleet. At the time of the flight from the Syndic home system, the Sixth Battle Cruiser Division consisted of the battle cruisers Polaris, Vanguard, Illustrious, and Incredible, commanded by Captain Badaya of the Illustrious.

Both Polaris and Vanguard were lost at the Battle of Vidha under the command of Captain Francesco Falco, leaving the Sixth Battle Cruiser Division extremely under-strength, compounded when Incredible was all-but-reduced to a wreck at Heradao.

However, Incredible survived to reach Alliance space and was subsequently brought back up to full combat capability at Varandal, where the Sixth Division was joined by a new Invincible, almost straight out of the Alliance's construction yards.

As such, after the Varandal Fleet reorganization, Sixth Division consisted of Illustrious, Incredible and Invincible, leaving it under-strength in comparison to the other battle cruiser divisions.

During the opening of book six, The Lost Fleet: Victorious, Admiral Timbale mentions that eight battle cruisers are to be added to Admiral Geary's command: the five Adroit-class ships (all assigned to Fifth Division), as well as Intemperate (assigned to Fourth), the new Invincible (assigned to Sixth, as above), and Insistent. Insistent does not show up in the Ships of the Alliance Fleet sections opening Victorious or subsequent books, and is only mentioned once further in the series (up to the end of Beyond the Frontier: Invincible, book two of the sequel series).

Since the Sixth Division is the only battle cruiser division with less than four ships post-Varandal, it is reasonable to assume that Insistent was assigned to it.

Amusingly, that one time Insistent is mentioned after Timbale assigns her to Geary, Insistent appears to be referred to as a battleship:

To Geary’s aggravation, two of the new battle cruisers, one of the new battleships, and several smaller combatants ended up pushing far forward of their assigned stations. “Adroit, Assert, Insistent, Dungeon, Pavise, Demicontres, Halda, Tschekan, assume your ordered stations immediately.”

The first three are known major combatants, and Dungeon and subsequent ships listed follow naming conventions for light combatants. However, Adroit and Assert are both Adroit-class battle cruisers of the Fifth Division, leaving Insistent as the third referenced major ship and, by elimination, the "battleship". However, the five battleships newly assigned to Geary are Dreadnought, Dependable, Sustain, Encroach and Resound.