Its use is rather limited due its short range and lack of direct fire capability it is primarily used on fortresses after the fortress's occupants are forced inside their walls. The Bombard is capable of ignoring cover when being used against fortified troops. Despite its comparatively short range, it is one of the most powerful artillery pieces in the Imperial Guard. The Bombard mounts a Siege Mortar on a Leman Russ main battle tank chassis. Warhammer 40K Darktide Review - Left To Shred
Consequently, Basilisks are often placed at the front of an artillery detachment. In the direst of circumstances, Basilisks may be used as secondary battle tanks if given adequate protection. Unlike the other artillery units in the Imperial Guard, such as the Bombard, Griffon, and Manticore, the Basilisk is capable of direct as well as indirect fire, giving it a limited ability to defend itself from enemy vehicles and infantry. Additionally, the guns produce a tremendous muzzle report, and it is also mentioned that Earthshaker crews tend to experience hearing loss. The Earthshaker shells are renowned for the powerful shrieking they make during flight, the mere sound of which is often enough to break enemy morale. The Basilisk can fire its main weapon directly at an enemy, but this means the Basilisk would have to be close to the enemy which is not good considering it is lightly armoured, instead the Basilisk will stay away from the main fighting and fire its weapon indirectly. Basilisks utilise the standard Chimera chassis but replace the passenger compartment and turret with the Earthshaker, leaving it with the hull-mounted Heavy Bolter weapon and driver's compartment. The Basilisk mounts one of the longest-ranged weapons in the Imperium's arsenal, the Earthshaker Cannon.
It is essentially an artillery piece mounted on a stripped-down chassis of a Chimera transport. The Basilisk is the most common artillery tank used by the Imperial Guard in the 41st Millennium.