HMS Sappho was a Royal Navy brig that gained public notoriety for causing a diplomatic incident over the slave trade with the United States of America and then went missing off the Australian coast in 1857–58.

Sappho was one of a large number of warships designed by Sir William Symonds that were intended to be both very fast under sail and carry heavy firepower.

This was reported to have been harsh as most of his senior officers were dead or in hospital due to (alleged) Yellow Fever and Mitchell was still suffering with a broken arm from a gunnery accident.

On the following day, the owner – J. P. Weeks – brought suit against the prize crew on the grounds of unlawful seizure, as a result of which they were arrested, and held in bail to $15,000.

On 18 September Sappho legally engaged a much larger slaver, the 1,088-long-ton (1,105 t) full-rigged ship Charles of New Orleans, about 40 mi (64 km) from Loanda, Portuguese West Africa, and drove it ashore – about 380 slaves were rescued but about 150 were drowned.

In October 1858, Admiral W Loring in Sydney was informed that Sappho had been seen by the crew of the schooner Yarrow off Cape Bridgewater, Victoria at the western entrance to Bass Strait on 18 February.

Between 1856 and 1860, three similar vessels went missing without trace and a fourth, HMS Camilla, capsized off the West Coast of Africa on 9 May 1859 with the loss of about 50 of her crew.