Home / Accueil

Power Cavern and Control Building

Canadian Air Defence Sector (CADS) Complex / Complexe du secteur de la défense aérienne du Canada (SDAC), Ontario, Canada

Formally Recognized: 2005/03/01

View of the mezzanine in the Power Cavern, 2004.; Parks Canada Agency / Agence Parcs Canada, Judith Dufresne, 2004.
General view
View of the main entrance to the Control Building, 2004.; Parks Canada Agency / Agence Parcs Canada, Judith Dufresne, 2004.
General view
No Image

Other Name(s)

Power Cavern and Control Building
Buildings 53 and 55
Bâtiments 53 et 55

Links and documents

Construction Date(s)

1959/01/01 to 1963/01/01

Listed on the Canadian Register: 2009/07/23

Statement of Significance

Description of Historic Place

The Power Cavern and Control Building, also known as Buildings 53 and 55, form the Canadian Air Defence Sector (CADS) Complex, a subterranean anti-nuclear bunker built 182 metres (600 feet) below ground level in the Pre-Cambrian Shield, located near North Bay, Ontario. It is composed of two units, constructed in separate caverns blasted into the granite, and connected to the exterior by two long tunnels, perpendicular to the complex. The designation is confined to the footprint of the buildings, caverns and tunnels.

Heritage Value

The CADS Complex is a Classified Federal Heritage Building because of its historical associations, and its architectural and environmental values.

Historical value
The CADS complex is one of the best examples of Canada’s joint participation with the USA in air defence during the Cold War and illustrates the country’s commitment to the North American Air Defence Command (NORAD), created in 1958. Taking five years and costing the Canadian Government over 15 million dollars to build, the CADS complex is the largest construction project in the region, and was co-financed by the US government. Its construction corresponds to a significant period of development for North Bay in the 1960s and lead to an important population increase. The bunker made the town of North Bay a “hot spot” and potential target of the Cold War, and also contributed to its physical transformation, as the rock excavated to create the cavern was used to improve the town’s waterfront.

Architectural value
The CADS complex offers an excellent functional design in response to very specific and demanding requirements. Armoured by the rock against a potential nuclear attack, the building acted both as a protective device and as a deterrent. Although it quickly became obsolete as a shelter with the increasing force and precision of nuclear weapons, the complex was meant to be completely self-sufficient, hermetical and flawless, so as to ensure the continuity of surveillance activities in a secure location where equipment could never fail. The bunker is one of the greatest achievements of the Royal Canadian Air Force (RCAF) Construction Engineering Branch, which coordinated the work of several private firms, namely A.D. Margison & Associates, H.H. Angus & Associates and Catalytic Construction Company of Canada.

The building’s aesthetic expression is linked to its functional design and the complex possesses certain unique qualities that speak to the will for survival and state of mind associated to the Cold War. All materials are well conserved, testifying to the quality of construction and continued care in the maintenance of the facility. In the efficiency of its design, rooting in the site, and stark, functional aesthetic, the CADS complex can be considered a “modern fortress”, not unlike the citadels built two hundred years earlier.

Environmental value
Because of its intentionally discreet nature, the CADS complex had little impact on its surroundings when built. It is therefore compatible with the undeveloped, partly wooded, military character of its setting, corresponding to the buffer zone which surrounds the complex above ground, between the base and Trout Lake. The general layout of the site and the two entrance portals have remained unchanged. The CADS Complex, known locally as “the hole”, is a familiar landmark for the community of North Bay. It holds an especially strong symbolic value, marking the town’s association with NORAD.

Sources: Judith Dufresne, CADS Complex (buildings 53 & 55, 56, 58 and 74 [four buildings]), Hornell Heights, 22 Wing, CFB North Bay, Ontario, Federal Heritage Building Report 03-110; 53/Power Cavern and 55/Control Building (2-Building Structure), Hornell Heights, 22 Wing, CFB North Bay, Ontario, Heritage Character Statement, 03-110.

Character-Defining Elements

The character-defining elements of the Power Cavern and Control Building should be respected.

Its exceptional functional design, a unique and extreme example of engineering, dictated by very specific and demanding requirements, as demonstrated in:
- its location deep underground, 182 metres (600 feet) below the surface in the pre-Cambrian shield, and the minimal number of openings;
- the access through long tunnels perpendicular to the complex;
- the configuration of the complex, divided into a three-storey control building and the power cavern, linked to the tunnels by galleries;
- security features such as the armoured steel doors which blocked off the entrance to the complex;
- the elaborate mechanical, electrical and other infrastructure systems, with their built-in redundancies, and the devices which would ensure complete autonomy in the event of an attack, such as the voluminous water and diesel reservoirs;
- the decontamination facilities;
- the clearly indicated evacuation routes.

The bunker’s aesthetic expression, intimately linked to its functional design, and which reflects the will for survival and state of mind associated with the Cold War, as conveyed by:
- the striking visual impact of descending into a “hole” deep below the surface;
- the contrasting quality of the omnipresent massive granite walls, dotted with reinforcing bolts and covered with chain link versus the flimsiness and lightness of the prefabricated steel panels and structure which form the shell protecting the more fragile electronic equipment;
- the simple industrial quality of the construction and materials, adapted from standard 1950’s designs and consisting of a “skin” and exterior systems;
- the starkness of the subterranean environment, which includes both the buildings and the cavern, reinforced by the use of grey-toned materials and finishes, with contrasting coloured elements associated to emergency services and exit ways.

Its use of standard materials and construction methods of the 1950’s, adapted here to the unique requirements of the facility, as exemplified in:
- the concrete and steel construction;
- the standard, economical finishes.

The bunker’s compatibility with the undeveloped, military character of its setting, and role as a familiar landmark for the community of North Bay, as evidenced in:
- the unchanged wooded area above ground, which bears no indication of what lies below with the exception of some surface equipment such as the air exhaust building;
- the well-known historical association, and strong symbolic value of what is known locally as “the hole”, which marks the town’s association with NORAD and the Cold War.




Recognition Authority

Government of Canada

Recognition Statute

Treasury Board Heritage Buildings Policy

Recognition Type

Classified Federal Heritage Building

Recognition Date


Historical Information

Significant Date(s)


Theme - Category and Type

Function - Category and Type



Civil Defence Site

Architect / Designer

RCAF Construction Engineering Branch



Additional Information

Location of Supporting Documentation

National Historic Sites Directorate, Documentation Centre, 5th Floor, Room 89, 25 Eddy Street, Gatineau, Québec.

Cross-Reference to Collection

Fed/Prov/Terr Identifier




Related Places



Advanced SearchAdvanced Search
Nearby Places