Introduced simultaneously with the Mark XVI , the Mark XVII was the "heavy" version of the same basic weapon system. Main armament was upgraded from a 50cm Hellbore to a 60cm weapon, and the ion-bolt infinite repeaters were increased to a total of fifteen (six each in two lateral batteries with a three-gun frontal battery in the glacis). The Mark XVI's mortars were deleted in favor of six 25cm howitzers and an increased missile armament. Weight increased to 6,500 tons, and maximum road speed dropped to 75 kph. The Mark XVII formed the 'heavy regiments' of the original Dinochrome Brigade .