The pirates who participated in the battle were Illanun Sulu, or Moro, pirates from the southern Philippines. They had raided several coastal settlements in 1862 and the years preceding so many men and women were being held prisoner or worked as galley slaves on board the pirates' prahus. A prahu was a type of large primitive sailing ship, with about a ten foot beam and usually over forty feet long, they could also be propelled by oars and the pirates armed theirs with three brass swivel guns each. The prahus had crews of over 100 men and were roofed by a bamboo cover to protect the ammunition and provisions from rain and to provide a platform to fight from. Sulu pirates sheltered in bays along the coast during the trading season to prey on merchant shipping passing from places like Singap