The Secret Military History of Manly's North Fort Plotting Room

Until 1952, the North Fort Battery featured two 9.2 inch calibre guns. Serviced by a network of underground tunnels, each was capable of firing a distance of 26.4km. Target coordinates were relayed to these heavy weapons from the nearby Plotting Room.

Located eight metres underground, the concrete-reinforced, bomb-proof Plotting Room is accessible via a camouflaged, shed-like entrance. Despite its name, the structure actually consists of two rooms – the Fortress Plotting Room (FPR) and the smaller Battery Plotting Room (BPR).

The Plotting Room was vital to Sydney’s coastal defences during World War II, receiving enemy craft intel from – and sending it to – artillery batteries located along the coast from Port Stephens to Port Kembla, collectively known as Fortress Sydney.

Target course and speed was sent via telephone from observation posts to the Fortress Plotting Room and then onto the Battery Plotting Room, which relayed coordinates to North Fort’s guns.

A member of the AWAS with a connection to the Harbour Trust was the late Patricia Talberg. In 1942, aged 19, she enlisted with the AWAS and was posted to North Fort. As an instrument operator specialist, Patricia manned the observation posts as well as the Plotting Room.

Today, Patricia's son Glyn proudly volunteers at the Harbour Trust’s North Fort Visitor Centre, where he greets people and offers them useful tips for exploring the historic site.

Although the young men and women who ran the Plotting Room were crucial to the Allied war effort, their story was not made public due to the highly classified nature of their service. In fact, to maintain the veil of secrecy around their work, the Army prohibited photography.

Except for a handful of photos captured by an official photographer in 1944, there is no other significant photographic evidence of the Plotting Room.

Thanks to the Harbour Trust's volunteer restoration workers, visitors are now able to descend into the Plotting Room – a rare example of an intact support building for Fortress Sydney – and discover the military secrets of this heritage bunker. How? By booking tickets for the Harbour Trust's Defence of Sydney Tour. Tours are led by knowledgeable volunteer guides including history buffs and former service people.

The challenge faced by the restoration workers was threefold...

Firstly, the Plotting Room is comprised of confined spaces eight metres underground with no natural light source. As such, the facility had to be made safe for people before the works could start.

Secondly, the Plotting Room was decommissioned after World War II and – during the decades of neglect that followed – the facility fell into disrepair.

Due to years of water damage, feral animals and general wear and tear, parts of the original infrastructure were beyond repair and had to be removed. Consequently, the restoration workers were required to source replacement materials that, as far as possible, closely matched the original fabric of the facility.

Thirdly, many of the Plotting Room’s original fixtures – for example, the plotting table, furniture, light fittings and pinboard wall cladding – had been removed when the building was vacated. Compounding this challenge was the fact that only limited information about the facility’s original set-up existed. As such, the few existing archival images were invaluable to the restoration workers.

To the extent possible, the original fabrics and fixtures of the Plotting Room, including the framing for the ceiling, were retained and stabilised by the workers. Where the original components couldn’t be salvaged or were missing, historical references were used to create faithful replicas.

These include the pinboard wall coverings, office area windows, metal fittings and the all-important plotting room tables. Further, the workers restored a World War II era ratemeter, reinstated the underground ventilation system, and painted a camouflage pattern on the exterior to enhance the visitor experience.

The Plotting Room project is part of a broader effort by the Harbour Trust to restore North Fort. Most recently, 18 restoration workers recreated North Fort’s underground engine room, which powered two 9.2 inch guns during World War II. Their work involved repairs to the engines, power distribution board and cooling tanks. In helping us preserve the site’s defence history, these specialist volunteers have also enhanced the guided tour experience for visitors.

Enjoy this video demystifying The Plotting Room and showcasing the efforts by specialist volunteers to faithfully restore it...

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Helpful links

1. Visit North Head Sanctuary
2. The history of North Head
3. DigiTale: Patricia Talberg
4. Defence of Sydney Tour
5. Read volunteer success stories