For some inexplicable reason, I was scrolling through the Cost Calculator the other day and came across some engineer tanks where the 'Extras' cost was 800 (fair enough) but there was also an additional 800 buried in the cross-add of Base + Ammo + ? = Cost + Extras = Total cost.
Rather than closing my eyes and backing slowly away - never to return - I wondered what this might be for, and saw that it affected a number of different unit classes ... ?
(USA OOB 12 Lines 196-199)