From Halopedia, the Halo wiki
The Elefen-pattern battlecruiser is a classification of warship employed by the Covenant. The Elefen-patterm, alongside the Ket-pattern, was one of the mainstay battlecruiser designs employed by the Covenant, succeeding the Maugen-pattern armored cruiser.
Little is known of the Elefen's design features. The ship was first namedropped in Halo: Warfleet – An Illustrated Guide to the Spacecraft of Halo and later again mentioned in the Halo Encyclopedia (2022 edition), though neither book have gone into any detail on the specifics of the design.
According to correspondences with Stephen Loftus, a common contributor to Halo source books, the Elefen namedrop was intended to serve as a definitive split between the design featured in Halo: Combat Evolved and Halo 2 (and its Anniversary edition) and that seen in Halo 3 and subsequent games. This split is reminiscent of the Syfon-pattern and Kerel-pattern assault carriers, though has yet to be corroborated in any subsequent looks at the ship. The Halo Encyclopedia uses both of the major variations on the page discussing the Ket-pattern battlecruiser and does not call out a specific ship as an Elefen, while Warfleet calls out the Truth and Reconciliation as a Ket-pattern - featuring it in its classic Combat Evolved design style with a smooth hull. This may indicate that the Elefen-pattern battlecruiser is in fact the battlecruiser design seen in Halo 3 and Reach - though thus far no source has explicitly confirmed as such.
Of additional note, Kenneth Peters (senior writer at 343 Industries and author of Warfleet and Halo: Fleet Battles) has explicitly confirmed that the number of sensor vanes on a battlecruiser is not an indication of design pattern differentiation - indicating that any identifying features of an Elefen would likely have to be more distinct.
- Halo: Warfleet, page 73: "The Zanar pattern is a stable mutation of the much larger Ket and Elefen pattern battlecruisers."
- Halo Encyclopedia (2022 edition), page 264
- Halo Encyclopedia (2022 edition), page 265
- Stephen Loftus on his talk page
- Halo Waypoint, Canon Fodder - Calm in the Storm (Retrieved on Aug 4, 2021) [local archive] [external archive]