Joseph Banfield made several slaving voyages to Africa. He rose to the rank of Chief Mate or second-in-command. Many sailors were forced onto slaving ships through trickery, but Banfield's autobiography shows that he chose his job. He accepted as his equal the African sailors and merchants he dealt with, but his attitude to the enslaved Africans in his care seems to be concerned more with their value than their humanity.

Slave ship captains had a reputation as hard men. There are many stories of their bad treatment of the crew. The crew members often joined a slave ship under duress, and the abolition movement used the high mortality rate amongst the crew as another reason for ending the slave trade. The experiences of the crew members were all different: some men seemed to enjoy their work, others suffered terrible treatment, many died of disease.

Joseph Banfield, a Bristol man, was Chief Mate on the Gambia under Captain Willis, and on other slave ships. He signed on for several slaving voyages: as a ship's officer he was perhaps treated better than ordinary seamen by the captain. His diary entries record the events of a slaving voyage in a very matter-of-fact way - he is not even sure how many of the enslaved Africans died during the gale, and he seems to think that the deaths of at least 20 enslaved Africans and the poor health of the others was important only because it affected their sale price in America.