Thickly vegetated and low-lying, the island faced the estuary of what the Europeans were to name Throsby's Creek after the first commandant of the Newcastle penal settlement.

Although steam cranes and coal loading staiths were provided, these proved problematic, and the mining companies began to press for better facilities capable of cheaper operation and easy expansion.

This plan, informed by the advice of long-standing residents of Newcastle, was part of Moriarty's highly ambitious scheme, evolved in 1858, for the transformation of Port Hunter from a swampy estuary to a deep water harbour.

[12] The building's materials are certainly similar to those of the Newcastle Customs House, in which Barnet and Spencer collaborated, and which was completed around the same time by the same contractor, and perhaps by the same workmen.

[16][1] At the time of its completion in 1878, the Bullock Island complex, consisting of the first stage of the Engine House, the first four cranes, and the first nests of railway sidings, was an industrial wonder dominating much of the port.

A "magnificent structure of solid handsome masonry, being built of white glistening sandstone blocks, beautifully dressed, from Sydney quarries, relieved by yellow brick masonry neatly pointed, and well and truly laid", the Engine House impressed many inter-colonial and overseas visitors and engineers, to whom it rapidly became a tourist attraction.

[17] The hydraulic accumulators developed the 800psi water pressure for the cranes' peak hoisting task, although the base load was provided by the pumping engines, originally of 100 horsepower, with 18-inch cylinders generating 90 psi.

These caissons were sunk some 40 feet into the river bed, the resultant spoil being manually removed and replaced by mass concrete, which would remain after the iron had rusted away.

[21] Second and third batches of cranes, this time mounted on cylindrical bases, allowed the government to concentrate most coal loading at The Dyke, which from 1881 was lit with gas.

"Hookers-on" then secured these chains to lugs atop the detachable timber, iron or steel coal hoppers or iron-braced timber coal boxes, which would then be "heaved" off their underframes and slewed over the ship's holds, into which the load was released through hinged bottom doors via a pin struck open by a sledgehammer-wielding "pin boss".

[22] The cranes, which revolved through 360 degrees on a heavy central bearing, were simple machines supported by massive iron pedestal and housings, the first four of which were supplied by Mort's Dock and Engineering Co., Balmain.

To support these, the Auxiliary Engine House was reconfigured as a condenser (battery) room, and a freestanding substation was erected to the north, apparently as part of a scheme for the complete replacement of the hydraulic cranes.

A heavily carved stone lion's head stands over the main entry, which is flanked by side bays with elongated arched windows, corbelled sills and prominent voussoirs and mullions, the latter featuring elaborate carvings of bunched roses, thistles and shamrocks, national flowers of three of the nationalities of the United Kingdom.

The stone architrave is surmounted by a frieze featuring prominent modillions supporting a cast-iron cornice, above which is a pediment with a simple tympanon.

7, 8, 9 and 10 form part of a group collectively illustrating the early application and progress of technologies historically important in the economic development of NSW.

7, 8, 9 and 10 are of state heritage significance for their association with Sir W. G. Armstrong and Company Ltd. and Cowans, Sheldon and Co. Ltd, engineering companies of world importance; with NSW government engineers Edward Orpen Moriarty; Cecil Darley; John Whitton; Percy Allan and Orlando Brain, and potentially with NSW government architect James Barnet and Edmund Spencer, one of his assistants; and with the public and private sector workers who constructed, operated and maintained the Bullock Island coal handling complex.

They may also be of state heritage significance as constituting landmarks of the public sector-driven transformation of Port Hunter from a swampy estuary to a deep water harbour of national importance.

7, 8, 9 and 10 are of state heritage significance in yielding scientific and archaeological information as to the nineteenth century transfer of hydraulic technology from the UK to NSW.

[1] Hydraulic Engine House and Crane Bases was listed on the New South Wales State Heritage Register on 25 August 2017 having satisfied the following criteria.

While the Engine House has been altered through the removal of plant, and three of the crane bases have been reused, they otherwise remain sufficiently intact to be fully legible to diverse audiences.

They also have a special association with the public and private sector workers who constructed, operated and maintained the Bullock Island coal handling complex.

They are associated with high levels of creative and technical achievement, both in their ability to house the state-of-the art machinery and equipment necessary for the development and transmission of hydraulic (and later electric) power and in their built form.

7, 8, 9 and 10 are of state heritage significance for their potential to yield further scientific and archaeological information as to Armstrong hydraulic plant in a maritime setting.

Information concerning the siting and operation of engines, chimneys and boilers is provided by footings, sub-floor voids, underground pipe runs and the like.

7, 8, 9 and 10 demonstrate the nature and application of nineteenth century hydraulic crane technology, and are of state heritage significance because of their unusual square shape.

7, 8, 9 and 10, which along with the railway complex and The Dyke demonstrate the nineteenth century transformation of Port Hunter by the public sector, and constitute benchmarks for understanding the generation and application of hydraulic power in colonial NSW.

7, 8, 9 and 10 are of state heritage significance as the only examples of their type in NSW, and provide rare evidence of nineteenth century coal handling via Armstrong hydraulic cranes.

They are intimately associated with the establishment of the Engine House, and demonstrate a defunct process formerly of great importance to the economy and society of NSW.

7, 8, 9 and 10 are of state heritage significance as fine examples of their type, exemplifying the principal characteristics of hydraulic and electric coal loading technology as developed and applied by Sir W.G.

As unique examples of their type in a NSW and Australian context, they are representative of diverse applications of the hydraulic system, and are outstanding in their setting and size.