Written by Kerryn Caulfield, Composites Australia Inc.
Australia’s military engineering history connects our industrial heritage with both our national past and contemporary identity. Archival preservation ensures these stories are safeguarded, allowing future generations to appreciate their significance and the contributions of civilian and military ingenuity to a rich legacy of scientific and engineering advancement. The AC Sentinel tank, Australia’s first and only domestically designed and produced tank, highlights this legacy. Its importance motivated John Belfield, founder of the Melbourne Tank Museum, to invest in its restoration, ensuring this remarkable feat of engineering is preserved for posterity.
Developed during World War II, the AC Sentinel was a response to Australia’s wartime isolation and the urgent need for armoured vehicles. Produced at the Chullora Tank Assembly Shops in Sydney, its design featured a fully cast hull and turret—an uncommon practice at the time. This offered greater structural integrity and simplified manufacturing, given the limitations of local resources. However, the project faced technical constraints, including a lack of suitable engines, which led to the innovative solution of combining three Cadillac V8 petrol engines into a single powertrain.
Between 1942 and 1943, 65 Sentinel tanks were produced. Despite their pioneering design, the Sentinel faced challenges with underpowered weaponry and operational limitations. Improved versions, such as the AC4 armed with the powerful 17-pounder gun, were developed; however, the program was discontinued—not due to inadequacy but because of the availability of American tanks and shifting wartime priorities. Today, only a few Sentinels survive, many deteriorated after decades of exposure.
The restoration of the Sentinel, commissioned by John in 2023, presented unique challenges. Due to cost and scale, traditional sand-casting methods used to fabricate the Sentinel’s original hull and turret was impractical for replication. Corrosion and wear on existing components further complicated the task, requiring creative solutions to restore structural and aesthetic accuracy.
JPM Shipwrights was commissioned to undertake the restoration. Managing Director J.P. Macquet utilised advanced composite materials and fabricating technologies to address the complexities of the project. While the lower half of the tank—comprising the tracks, suspension system, road wheels, idler wheels and rollers—remained original and intact, the restoration focused on the precise replication of the tank’s top half, including the deck, turret and driver’s cabin.
A challenge was replicating the intricate ‘as-cast’ surface texture of the hull and turret while maintaining structural integrity. This texture, a distinctive feature of wartime sand-casting methods, presented a unique obstacle. Unlike standard restoration efforts that often aim for a polished finish, this project prioritised authenticity, demanding a faithful recreation of the Sentinel’s dull, grainy surface. The result was a restoration that not only preserved the historical integrity of the AC1 Sentinel but also honoured its unique wartime production characteristics.
Composites were chosen as the primary material for this restoration due to their versatility, strength-to-weight ratio, and ability to replicate fine details. The process involved:
- Precision Moulding: High-detail moulds were created from surviving Sentinel components to capture the texture and geometry of the original cast steel.
- Material Selection: Durable composite materials matched the structural requirements while being lightweight enough to handle and install efficiently.
- Surface Treatment: After moulding, coatings were applied to replicate the appearance of oxidised steel, simulating the original tank’s aged patina. This step was critical for maintaining historical authenticity.
- Testing and Validation: The restored components were tested for durability and fit to meet functional and aesthetic standards.
J.P. explained, “It was the reverse of the concourse finish required for racing yachts. Instead of perfection, we had to embrace the imperfections inherent in sand casting and replicate them faithfully. Composites allowed us to achieve this with precision and cost-efficiency.”
At 93, John Belfield’s fascination with military vehicles remains as vibrant as ever. His passion began during his school years in Melbourne, where encounters with US soldiers on leave and being part of a cadet program sparked his curiosity. Early memories of carrying a cadet rifle home on the tram laid the foundation for a lifelong dedication to preserving Australia’s military heritage. This passion culminated in the creation of the Melbourne Tank Museum in 1993, a remarkable showcase of military vehicles and artefacts spanning decades and continents, each telling the silent story of engineering and innovation.
“Although I sold much of my collection in 2006, I remain committed to restoring and preserving what matters. The AC Sentinel tank is an important piece of our heritage—a tribute to the connection between engineering and Australian history, ensuring our past is safeguarded for future generations,” John Belfield.
Cruiser tank
- Crew 5 (Commander, Gunner, Loader/Operator, Driver, Hull MG gunner)
- Armour Hull front 65 millimetres, sides and rear 45 millimetres
- Turret 65 millimetres all round
- Primary armament 2 pounder tank gun, 130 rounds
- Secondary armament two .303 (7.7 mm) Vickers machine guns, 4,250 rounds
- Engine 3 x Cadillac V8
330 horsepower (246 kW) - Suspension Horizontal Volute Spring
- Range 240 km
- Speed 48 km/h
The AC in AC Sentinel stands for Australian Cruiser, following the British tradition of classifying tanks by operational roles. Australia’s cruiser tank was designed for speed, flanking manoeuvres and exploiting battlefield breakthroughs. The name Sentinel, related to “sentry,” signifies vigilance and perception, reflecting its role as a “watchful guardian” and protective force during a time of vulnerability in World War II.
