Optical Munitions

 

At the outbreak of the second world war, Australia found itself very short of optical munitions. These are glass lenses ground by experts from the most pure and optically precise glass. They are used in range finders for artillery, gun-sights on aircraft and periscopes on submarines. Germany held an almost complete monopoly on this strategic knowledge at the outbreak of the WWI (Zeiss). At the outbreak of WWII Japan had much better optical glasses than Australians.

Our sand and glass had traces of iron and manganese, elements that caused clouding and as such were not of high enough grade to use in making lenses for telescopes and gun-sights. We had the people who could grind the lenses but not the glass to grind. The UK and the USA, upon whom we had relied for such raw material, understandably, put a ban on their export upon the outbreak of hostilities.

Yet after only 6 months of war, Australia had some of the best optical munitions available. The defence department made the following order, which was filled:

  • Tank periscopes: 10,000
  • Dial sights: 68,000
  • Anti-tank gun sights: 46,000
  • Rifle sights: 39,000
  • Cruiser tank gun sights: 15,600
  • Naval gun sighting telescopes: 8,600
  • Anti-aircraft predictors: 8,400
  • Aircraft identification telescopes: 3,300

At the same time as this order was filled Australia supplied the following amounts of optical glass to other nations:

  • USA : 57,000 lbs
  • New Zealand : 4,700 lbs
  • India (slab glass) : 5,200 lbs

The company that did most of the work (with significant help from university physics and chemistry departments, and possibly agricultural soil departments) was Australian Consolidated Industries (ACI), the local subsidiary of Imperial Chemical Industries (ICI) that ran a glass factory in Waterloo, now a car sales office and residential flats.

Botany Bay was on their doorstep and there they found a pure white, bleached white sand that was pure enough and depleted of almost every other element to make optical munitions.

This amazing piece of applied industrial research and development was made possible by the existence of this very interesting sand deposit at Kurnell on Botany Bay.

The sand used was the A2 horizon of a Giant Podsol, a type of soil with a few distinct layers. On top is the often black organic material layer called the A1. Below this is a bleached layer where the minerals have been leached out into the soil below. This bleached layer sits ontop of a usually heavily coloured layer full of the iron or aluminium leached out from the layer above.

All these soils have gone from Kurnell now as the place has been mined for sand for close to 200 years. The bleached A2 horizons of the soil profile developed on top of this Aeolian sand is amongst the purest silicate sand known anywhere in the world, being almost totally leached free of iron (Fe) and titanium (Ti). It took nature thousands of years to rid this layer of colour.

Had this area not had some of the purest silicate sand in the world, would the outcome of the war changed?

This post was co-authored with Simon Leake. 

Podosol image from QLD Government

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