Cluster Shells are special munitions fired by Long Tom, Sniper and Thumper artillery. The shells are designed to explode in mid-air, showering the area below with miniature bomblets. Cluster shells are particularly adept at inflicting damage on an opponent attempting to take cover within defensive positions.
Infantry in a hex hit by Cluster ammunition are considered in open terrain regardless of any defensive fieldwork, while 'Mechs and other vehicles resolve such hits as a Shot from Above. Units hiding within a building are protected, although the building itself may take damage as per normal rules.
- Tactical Operations, p. 354