Published on Australian Maritime Safety Authority (https://www.amsa.gov.au)
These maps are not secret.
The figures of 69 kilometres (37 nautical miles) and 89km (48 nautical miles) reflect surface and aerial observations made at the time.
However, while the figures quoted on these maps are accurate, these maps were produced as power point slides for briefing material and are not to scale.
Consequently these maps cannot be used to extrapolate accurate distances.