[4] 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.

Armed with three brass swivel guns each, they 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 Singapore, Penang, or China back to the Americas or Europe.

So when he arrived at Bintulu the labourers were put ashore to construct the fort and ten Sarawakian soldiers joined the Rainbow's small crew to strengthen it before the coming battle.

The Sulus themselves were heavily armed with muskets, pistols, swords, knives, spears so the men of the Sarawakian vessels placed mattresses and other improvised bulwarks on the upper decks to protect their legs from "ugly hits" according to Bishop Francis Thomas McDougall of Labuan, who was present during the battle on board the Rainbow.

The water was shallow and the Rainbow had the Jolly Bachelor in tow; her captain, the Rajah Muda, intended to release the smaller ship as soon as they were in a good firing position.

[9] Captain Brooke's plan, after casting off the Jolly Bachelor, would be to ram the prahus while keeping them engaged so as to prevent the pirates from boarding and overwhelming the Sarawakians.

McDougall wrote; "Our plan of action was to silence the brass guns with our rifles, to shake them at their oars with grape and round shot, until we could run into them without their being strong enough to board us.

The steamer was kept dodging about within range until the time came to run in; then we got into a good position to put on all steam and given them the stem, which was always admirably and coolly done by Captain Hewat whenever the order was given by the Rajah Mudah."

After an hour the weather was very calm and a lookout at the masthead spotted the three enemy ships to the starboard, lining up to bear their bow guns on the approaching steamers.

As the Sarawakians neared the pirates they opened up with their swivels but Brooke waited until his ships were 250 yards away before he gave his men the order to return the fire.

The prisoners could not escape because if they had a chance to jump over the side, the Sulus had a three barbed spear ready and if struck by one the victim could "no longer swim nor run" and would either drown or be retaken.