Maritime history buffs are celebrating a little-known part of Victoria's history today, marking 150 years since a ship involved in America's civil war arrived at Williamstown, in Melbourne's south-west.

The civil war was fought between the Union, known as the Yankees and based in the north of the country, and the Confederates, in the south, between 1861-1865.

The Confederates' CSS Shenandoah was a raider ship used to disrupt Union supply ships, destroying dozens of ships, seizing goods and imprisoning merchant sailors.

It began its journey in England and was in the southern hemisphere searching for American whaling ships when it needed repairs.

The crew had only two options for the stopover: Cape Town, where the crew was likely to come across Union ships, and Melbourne, where the likelihood of crossing the enemy was low.

So the CSS Shenandoah docked in Melbourne on January 25, 1865.

During its visit 42 Melbourne men secretly joined the Shenandoah's crew before it was sailed back out to sea to continue its attack on the way to the US, providing a rare Australian link to the war.

Four cannons were fired at midday at Williamstown on Sunday to mark the arrival of the ship.

One of the organisers of the commemoration, Peter Hemphill, said the visit had world significance.

"It destroyed the whaling fleet of the US, it had also fired the very last shots of the American Civil War," he said.

"It's important because it's the only real link to America's civil war in Australia.

"The ship started out known as the Sea King. It was bought by the Confederate navy secretly in England in late 1864.

"It was spirited out of England off the coast of Africa, they changed its name to Shenandoah, loaded it with cannon, with supplies and marines.

"[It] sailed to Australia and sank eight Yankee ships on its way. The captain, James Waddell, was trying to meet up with a mail run that was leaving Melbourne for the United States so he could report back to his commanders so they knew where he was at.

"He also needed repairs to his propeller. In the meantime the Yankees ... tried to get them arrested as pirates."

Australian recruits join the Confederate fight

Mr Hemphill said at one point ship was surrounded by Australian police and military after accusations it was recruiting men, which was not allowed.

The crew spent time in Victoria, visiting the Melbourne Club and also Ballarat, where they held a "buccaneer's ball".

A map showing the route the Shenandoah took on its way to Melbourne from England. ( Supplied )

"When they left 42 Melbourne men bobbed up on deck and they were part of the crew that for the rest of the journey," he said.

"They went up to the northern Pacific and created havoc - just destroyed the Yankee whaling fleet.

"They needed whale oil for greasing their cannon wheels and so forth, but it absolutely devastated the fleet for years to come.

"Part of that was after the war had ended. They sailed down the US coast and they found out the war had ended so they then stowed cannon in the hull ... and basically surrendered."

Mr Hemphill said seven years later the ship and crew, including the Australians, were involved in a court case brought by the United States against England, accusing them of assisting the Confederates.

"In the end Britain had to pay US$15.5 million in gold coin, which is worth billions today," he said.

"So it has a lot of significance in the world. It also fired the very last shot of the civil war."