Why worry about an obsolete Mark V tank?

Why would German planners worry about Mark V tanks when their armor was inadequate?

The concern was their possible use with altered weapons or protected firing positions, where their original armor would not determine the whole threat.

A Mark V's original armor was only one part of the possible threat during an invasion. German concern centered on changes to armament and use from prepared defensive positions. Concrete or earth cover could make an old vehicle a more difficult obstacle than its armor alone suggested. The example is a possible emplacement blocking a road, where concealment could also delay an attacker's response.