The national flag of a ship is also taken into account when choosing a target, with British vessels being increasingly avoided, according to the report.
Tourism was boosted, as were sales of Union flags and mugs. But this effect appears to have been wiped out by the extra bank holiday, which encouraged many factory owners to suspend plant operations.
As the death toll grew, there were poignant scenes at Wootton Bassett, Wiltshire as five coffins draped with the union flag arrived at RAF Lyneham and were met by sombre crowds on the town's streets.