As everyone knows, Mount Stromlo Observatory (and its history) is intrinsically linked to the stars and many people hold it in a fond place among Canberra's local community because of its fascinating history. But what some may not know is that the site was also used as an Optical Munitions Factory during World War II.

A tangible example of this - a gunsight which contains a 1944 mark III 60 millimetre lens for a 25 pound quick firing cannon - now sits proudly in a display cabinet inside the Mount Stromlo Visitors Centre.

As it turns out, Mount Stromlo was one of three government-run facilities that the gunsights (or devices that are used on weapons to allow them to be aimed accurately at targets) were made.

At the time, Stromlo was the only factory in Australia that designed, manufactured and tested all their gunsights in one location.

Astrophysicist Dr Brad Tucker, who was responsible for overseeing the gunsight's acquisition, calls it "one of the last relics of an important, yet often forgotten era of Mount Stromlo."

"The US and UK were supposed to supply optical munitions for the ANZAC's but the shipments never came. Therefore, Parliament turned to us [the then Commonwealth Solar Observatory] to help them," he said.

"It was so secretive that the records never made it to the National Archives and so not even the War Memorial keeps this history - it is only known through internal records, files, and stories. Scientists and engineers fleeing Europe who settled in Australia found a way to help the war effort through supporting the work that was done here."  

The gunsight was acquired by ANU last year via a private collector and now sits on display as a reminder of another (albeit brief) role the facility played in Australia's history.

Dr Tucker says the optical munitions work also paved the way for the Observatory's continued success well into the future.

"Our optical munitions history that allowed us to make our large telescopes that we started to populate Mount Stromlo with in the late 40s and 50s as we had quickly developed a history and expertise in precision optics," he said.

"This gunsight is a small hidden gem from an activity that ultimately helped make Mount Stromlo one of the world's great observatories and astronomical institutes."  

The process of creating a gunsight lens - documented through a series of 12 photograghs taken in the 1940s - can be viewed via the Australian War Memorial's online archive.

Do you know a hidden gem located somewhere on the ANU campus that you'd like to share with the community? If you do, we'd love to hear about it. You don't have to know much about the object's history as we can do all of the background research. If you have a Hidden Gem idea, drop us a line at on.campus@anu.edu.au.