The Bolo Mark six was a direct descendant of the Mark III "mobile firebase" concept. While it had the same power plant and computer support of the Mark V , its railgun main armament was replaced by a VLS missile system. To compensate for the lack of a railgun, the 60mm infinite repeaters were upgraded to 7 guns per side. The Mobile Firebase Concept was the PreCursor, the actual "First Inkling", of the "PLANETARY Siege Unit" which required the VLS Missile as it's main Primary Weapons System.