One is clearly how HMAS Sydney, a crusier with a combat-experienced crew just returning from the Med ... was sunk by a surface raider - basically a freighter hull as a gun platform - no armoured decks, ..., etc.
Two, why the circumstances re: HMAS Sydney have been classified for so long.
Of interest by these lights will be the release of undersea photographs.
My great uncle went down on the HMAS Sydney. My Father who was six at the time was actually re-named in his honor.