Providing a safe, all weather harbour for the capital of Perth was his first job. He proposed an inner harbour in the mouth of the Swan River. There was a great reef in the entrance that was a problem. The prevailing 'expert opinion' also reckoned that sand movement in the area would cause such a harbour to silt up quickly. But he did his homework and found that such sand movements were not the problem that they had been made out to be, and that the reef could be blasted out. He proposed two breakwaters to protect the harbour from the seas.
If John Forrest needed O'Connor, so O'Connor needed Forrest. He presented the WA Government with detailed and costed plans for the new Fremantle harbour. It needed a man of the stature of Forrest to get it through Parliament and to get the funding organised. It took five years to get the job done - a pretty amazing accomplishment, given the very limited machinery available in those days! Construction started in 1892 and was finished in 1897.
That same Fremantle Harbour is still in use today, 121 years later, though it has had an extension or two since then. The critics were wrong, the harbour hasn't silted up, and Fremantle is the major port in Western Australia. He was awarded the Companion of the Order of St Michael and St George for this job. This award showed the value of his work, as it was recognised internationally. It didn't stop the critics, though, as we shall see!
Eventually the value of his work was recognised and a statue by Pietro Porcelli was erected near the Fremantle harbour in 1912.