From earlier posts;
The Germans would have been flying a false flag (until or till just before the moment they opened fire). They would have been doing everything possible to appear as an innocent noncombatant. How was the Sydney to be 100% certain as to the identity of the German ship under those circumstances? Was there any way for them to be 100% certain, short of boarding the Kormoran?

and
The Kormoran was doing its level best in obfuscating its signal replies to Sydney's demands for identification.

The documentary mentioned it only in passing and didn't expand on its significance but I seem to recall the documentary including words to the effect that the first of Kormoran's salvoes destroyed not only the forward gun turrret and the bridge, with its control centre, it also destroyed the Sydney's Walrus.

From memory, the Walrus was a seaplane carried on deck, normally lashed down until deployment by being hoisted overboard by derrick; again from memory, it was capable of carrying out aerial reconnaissance for its mother ship.

It struck me that the Walrus could have been deployed from beyond the Kormoran's range but it also struck me that the camouflage used by the Kormoran may have been adequate to disguise its identity and armaments from aerial observation as well as from a purely horizontal examination by other ships.

Perhaps those of you familiar with Q ships might be able to shed light on this aspect.

Cheers, Rowan