Duke and Turk were originally Captain Wilhelm's dogs until the ship the Robinsons were on was chased into a storm by Kuala and his crew and found itself stuck on rocks which weren't too far from land.
Francis, the Robinsons' youngest son, insisted they bring Duke and Turk with them to the island, despite Father's fears that they might sink the raft they made and sailed on. But fortunately, they don't do so when Father finally allows them to climb on.
The following day, Duke and Turk help Mother search for Francis, who had found a baby elephant he named Rocky, while at the same time fending off the tiger that was on the island.
On the day of the Robinsons' new holiday, Turk was one of the animals who participated in the race with Francis' monkey riding him, along with Rocky the elephant (ridden by Francis), Lightning the mule (ridden by Fritz), Clementine the ostrich (ridden by Ernst), and Duchess the zebra (ridden by Roberta), while Duke stood with Mother and Father.
During the race, after Duchess lead Roberta to the beach where she spotted the pirates coming ashore to look for her since she was their former prisoner mistaken for a boy at first, Duke and Turk were seen running back and forth while chasing Duchess; probably trying to bring her back to the Robinsons. Then, Duke and Turk were later called by Francis with a whistle, which gave away the Robinsons' whereabouts to the pirates, and joined them on top of a hill where a battle against the pirates was about to occur.
In the end, after the pirates' deaths, and as Ernst travels to England with Roberta's grandfather, Captain Moreland, to continue his education there, Duke and Turk were last seen running away along with Clementine, Duchess, and Rocky as Francis tried to bring them back.
Turk's muzzle is more black than Duke's and he has a white belly and black rings around his eyes, unlike Duke.
In the original novel, Duke was a female dog named Flora.
According to director Ken Annakin, eight different fawn dogs were used to play Duke and Turk; one was capable of hunting, one was capable of facing a tiger, one was a great swimmer, and the other would follow. For the tiger fight scene, the hunting dogs were really chasing it.