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I'm sure we have some people here who know a bit about aerial photo interpretation, so You may be able to assuage my and my neighbours' curiosity. The attached photo shows part of our area, now a NW Sydney suburb, taken in 1943. In the centre right of the photo is a circular array with something in the centre. The diameter of the circle is approximately 37m, and the approximate length of the longest structure in the circle, at the south, is 6m. The road running approximately Ne-Sw is on the ridge line, and the land drops away fairly steeply from about the location of the circle. The light area on the left of the photo is a sandstone quarry. The land south of the circle out of photo was a sewage disposal area. but I'm pretty sure it never extended as far north as the circle. Further south were orchards and chicken farms (not a euphemism.) The largest trees in the area would be 20-30m high I think. It's possible, though I haven't found any evidence, that the area was used by the military at the time. I don't know the date of the photo, but I'm guessing it was close to the winter solstice.
The area is now covered by houses and no evidence of the circle is visible.

Speculation or informed advice on what the circle is would be welcome.

I would suggest an HF radio relay station, given the high and accessible location.

Was VOR invented when that was built?? Looks a bit similar to a modern system.

The Ancient Mariner

Fox3WheresMyBanana wrote: ↑

Fri Jan 05, 2024 10:06 am

I would suggest an HF radio relay station, given the high and accessible location.

Was VOR invented when that was built?? Looks a bit similar to a modern system.

Iit could be something to do with air navigation, as it's on the northern approach to Bankstown airport, which was in use during the war. It's about midway between the current Hornsby & Pennant Hills strobes.

They started developing VOR in 1937, and the Americans did have a liking for trying things out dununda, out of sight of prying eyes.

Anything to do with this, perhaps?

https://en.wikipedia.org/wiki/Bankstown_Bunker

llondel wrote: ↑

Sat Jan 06, 2024 3:13 am

Anything to do with this, perhaps?

https://en.wikipedia.org/wiki/Bankstown_Bunker

It could be associated with the airport, as it's on the northern approach, and the bunker was also associated with the airport. I doubt that there's a direct association.
When I was a kid we spent a lot of time riding around in that area, as it wasn't far from home and I had a few mates who lived nearby. Our road cycling circuit was also nearby. We weren't aware of any bunker there then.

Edit: Apparently there was an artillery unit in the area, and a spot about 500 metres from the feature was supposedly used as a target for mortar practice. I wonder if it could be related to that?

Could be a CDAA. Maybe part of Australian SIGINT in Sydney during WW2

I doubt that it's CDAA, the circle doesn't seem to be composed of antennae. Sigint, possibly, but doesn't seem to be concealed as I'd expect. It's almost like the circular structure is intended to be seen. Could it be a visual navigation aid? Did such things exist?

Can you relate the photo to a current street map?

John Hill may be your man for this??

Best guess, foundations for a water tank.

Boac wrote: ↑

Sun Jan 07, 2024 11:54 am

Can you relate the photo to a current street map?

Yes. The location is now under a suburban street and there is no evidence of it visible. I walked the area before there were houses there, but didn't notice anything, though I wasn't especially looking. At that time, the remains of the quarry were there, but now even that's not evident.
John, foundations for something sound reasonable, but there's no evidence now that there was one there, and a tank that size (~37m dia) would be unusual in the area. Still, it may have been related to the quarry.
The area at that time was mainly agricultural - orchards, dairy and poultry. I thought of low poultry sheds, but they usually seem to be layed out in rows rather than a circle.

Yes. The location is now under a suburban street

Could you tell us that location?

See the attached Google map screenshot. The location is approximately where the pin is on Russell Cres. Westleigh.
The 1943 map is from [attachment=0]Screenshot 2024-01-08 at ... qXksKtyddI

Correction: Link for the 1943 air photo is https://maps.six.nsw.gov.au/?fbclid=IwA ... 4HNKlmekMI Location is Westleigh and base map is 1943.

There was nothing much there in the 1960s - I used to live just over a mile east of the point.
We used to go adventuring in the valley just east of the hill.

Fox3WheresMyBanana wrote: ↑

Mon Jan 08, 2024 1:30 pm

There was nothing much there in the 1960s - I used to live just over a mile east of the point.
We used to go adventuring in the valley just east of the hill.

You wouldn't recognise where you lived now. It's no longer lots of bush. Mrs Hydro grew up there too.
The quarry is now a money pit as the council was lumbered with the clean-up costs, and has been turned into a park. https://hornsbypark.com.au