In the crews of ships that transported Africans across the Atlantic to the Americas, free black men worked with white men, and occupational and class ties often cut across racial lines, writes Emma Christopher.

I am used to the stony faces staring back at me as I speak. The audience, especially at North American conferences, rarely looks accepting of my research. The events might have taken place more than 200 years ago, but they remain alive in the minds of African-Americans, and the question of monetary reparations is a political hot potato.

The slave trade, those faces seem to say, was an atrocity founded on racial inequality - but studying the sailors who worked in the slave trade tells a rather more complicated story, one that many people are understandably uncomfortable with.

The 1785 rebellion on the slave ship Amity illustrates the point well. It happened when the ship was heading east across the Atlantic Ocean from Virginia towards the African landmass. Two slaves known as Dick and Will were involved. Having left the African continent one year before, they were labouring as seamen on the Amity at the time they rebelled, or "turned pyrate", as their contemporaries may have phrased it, for their captor was later their captain.

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Dick and Will's fellow mutineers are equally fascinating for they really were a "motley crew". There was a mulatto Bostonian named Stuart who sported a cut on his nose and a scar on his forehead. John Mathew and Alexander Evans were Irishmen, reported, in stereotypes common to both their nationality and their profession, to "have a good deal of the brogue" and to be "very subject to liquor". Richard Squire was an Englishman who claimed to have been a lieutenant on the USS General Washington. The last known rebel was John Boadman, described as having a "black complexion" and being "about five feet seven inches high". Equally interesting, perhaps, is the ethnicity of those who were cast off in the ship's longboat. As the rebellion progressed, the captain, mate and boatswain were set adrift along with three "black boys".

Free black sailors, white men rebelling on board slave ships - this is hardly the image of the slave trade usually portrayed in popular and scholarly accounts. Admittedly, the numbers involved in this kind of interracial rebellion were minuscule compared with the numbers who were transported as African captives just one way across the Atlantic. But the fact of the slave trade, no matter how unpalatable, is that it was a trading network. As such, it employed a racially diverse group of men. The ships taking part in deep-sea trades have always involved the exchange of workers as well as of goods, disease, culture and genes. Just as Lascars (Indian sailors) worked on ships of the East India Company, having been caught up in the international trading systems moving cotton and spices across the globe, so Africans and African-Americans joined slaving vessels as free workers as well as unwilling merchandise.

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Crew lists from slave ships that left American ports in the very last years of transatlantic slave trading still exist. They suggest that the men of the Amity, not only the slaves Dick and Will, but also the free black men Stuart and Boadman, were hardly unique. Listed under the "complexion" section in the muster rolls of Rhode Island slave ships can be found men described as "black", "brown" and "mulatto yellow". Seafaring was, after all, one of the only occupations open to free blacks in 18th-century America - many whaling ships' crews were about half African-American. It is hardly surprising that these men who were so discriminated against were sometimes forced to accept any employment they could find, even if it was in the morally repugnant slave trade.

For slaves such as Dick and Will, there was little choice. They were hardly unusual in being enslaved men working on slave ships. American slaveowners hired out their bondsmen to captains as sailors in order to collect the wages they would earn. Bristow Champlin, who was hired by the ship Adventure in 1766, earned more for his owner during the course of the voyage than his fellow sailors earned for themselves. A slave named Sippeo, employed by the slaver Resource, was able to cut into his earnings to buy himself some "spare trowsers" before the ship returned home.

There is no doubt that these men were discriminated against, holding lowly positions aboard ships throughout their seafaring careers. Their European co-workers often held ambiguous sentiments towards them - they treated them with egalitarianism unheard of among 18th-century shore-based society, but still on occasion saw them as inferior.

As an occupational group, seamen paid less heed to racial differences than most. They also viciously quelled slave rebellions, raped enslaved women and committed many other untold atrocities against Africans. Sometimes, as the Amity rebellion illustrates, the occupational and class ties of seamen cut across the colour line.

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North American slave ships were not alone in the practice of hiring sailors of African origin. Slaving vessels that left from the British Isles, France and Portugal also had such men employed on them. Brazilian slavers had the most: historian Herbert Klein found that 42 per cent of the men employed on slavers leaving Rio de Janeiro between 1795 and 1811 were of African origin.

Despite those stony faces, the last thing I believe this research does is to justify anything that happened in the slave trade. That, unquestionably, was a crime against humanity. Rather, these men draw attention to the diversity of the African experience in the Americas and to the perverse twist of fate that meant that some of them had to return to the slave trade as free men in order to feed themselves.

The story of Thomas Lee reminds us why these men should not be forgotten. An African-American employed as cook on the Sarah in the 1700s, Lee testified to the Admiralty Court that sick slaves had been thrown overboard for financial reasons. He, alone among the crew, spoke of it as "bloody murder".

Emma Christopher is completing her PhD thesis - about sailors employed in the transatlantic slave trade - at University College London.

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