It seems 'campaign problems' has become the new 'no crew eyes' bug to beat legitimate purchasers with the big piracy stick
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The mission requirements sometimes have sub-requirements that aren't listed. In the War Materials case, it says that you need to sink shipping that is carrying 'War Materials' cargo to Britain, or something like that, so sinking warships won't have any effect and possibly outbound shipping won't be counted. If the ships are empty and have no cargo, they also won't count. There may also be further requirements on what type of shipping you need to sink.