The secret history of West Block

But there is a secret history about the place and particularly the small, innocuous structure tucked away behind the main building. This small structure has quite a remarkable story to tell - a story involving national secrets, encoding and decoding, and a small group of people, mainly young women, who worked in its very confined space during the Second World War.

The young women called themselves the 'Cable Girls' and the building, the 'Bunker' or 'Dugout'.

During the war West Block housed the secretariat staff of several major government departments, including the Prime Minister's Department. Within the Prime Minister's Secretariat was a section responsible for the encryption and decryption of the Prime Minister's Department and External Affairs communications.

In the days well before highly secure online digital encryption of messages, the main means of communication between the prime minister and foreign heads of state was by encoded cablegrams, often sent overseas on land/sea lines and radio links.

In times of war, these links were subject to interception by the enemy. One way to provide security of these communications was to encrypt the plain language messages at their source, transmit them in code via the cable links where they would be decrypted back into plain language by the recipients.

The Cables Branch had begun as a small group of officers, mainly female. But during the Second World War, with the escalation of the conflict into the Pacific area and the southward advance of the Japanese forces, the amount of high-level security cables that had to be processed in the Bunker increased, putting pressure on the efficiency of the current staff.

Subsequent staff increases and extra space in the main West Block building had to be made while still maintaining strict security requirements.

Prime Minister John Curtin saw the importance of the Cables Branch, and their capacity to maintain the enormous load of encrypting and decrypting, as absolutely vital to the war effort.

The small Bunker and the 'Cable Girls' played a part in one of the defining moments in Australian history and the relationship with Britain.

Following the fall of Singapore to Japanese forces on 15 February, 1942, Curtin - who had only been in office since October the previous year - cabled Churchill requesting that the Australian 6th and 7th Divisions, then serving in North Africa, be returned home to defend Australia.

However Churchill, mindful of the potential threat to India by the Japanese, tried to divert the Australian troops to Burma. What followed was a tense period of terse cables exchanged between the two leaders, with the United States President, Franklin D. Roosevelt siding with Churchill.

Curtin maintained his ground against these two powerful leaders and the Australian Divisions were returned home. The cables exchanged between these leaders were encrypted and decrypted by the Cable Girls in the Bunker.

Nancy Metcalfe (nee Ward) was one of the young 'Cable Girls', coming to Canberra from Adelaide in 1941 and soon found herself encrypting and decrypting the high-level communications between Prime Ministers Curtin and Churchill in a time of national crisis.

Nancy lived to be 94, dying in 2015 in Canberra, just days after her husband, Ron, who was 95. In her unpublished memoirs she recalled:

"Cables were pouring in. Some were far from interesting, but I felt proud to be doing the few which were addressed 'Most Immediate', and 'Most Secret', 'Churchill to Curtin' [and] 'Himself Alone' ... Early on, I always had to do the most secret ones. I have since wondered if I had been security checked beforehand. Perhaps my two years with the Navy gave me an 'all clear."

Today, the Bunker, along with the West Block building and the Parliamentary Triangle, are on the National Heritage List and are under statutory protection.

But a visitor wouldn't realise the vital operations that occurred there during the days of the Second World War. The Bunker deserves a wider recognition.