Captain Haddock's friend Captain Chester is captain of the Sirius. When there is no fuel available for the Aurora (the ship used on the expedition), Tintin and Captain Haddock decide to siphon fuel from the Sirius. Bill is the ship's cook on this voyage and is angry at Snowy who steals food on several occasions.
When Tintin and Captain Haddock are planning the expedition to find the treasure of the Unicorn, Haddock decides to ask Captain Chester if they could use the Sirius for the expedition.
Tintin and Captain Haddock take the Sirius on their expedition to find Red Rackham's Treasure. The ship is equipped with a pump which the Thom(p)sons manually turn to supply air to Tintin, and later Captain Haddock, as they use the diving suit to explore the wreck of the Unicorn. Bill is the ship's cook on this voyage. He blames Snowy for stealing a box of biscuits and a chicken (as he had stolen food on the Aurora in the Shooting Star) but this time the food turned out to have been stolen by Professor Calculus, who had stowed away on board.
- Captain Haddock's friend Captain Chester is captain of the Sirius, in The Shooting Star. In The Secret of the Unicorn, when Tintin and Captain Haddock are planning the expedition for the treasure, Haddock decides to ask Captain Chester if they could use the Sirius for the expedition.
- The Sirius, was named after the SS Sirius, the first ship to cross the Atlantic Ocean solely under steam power, but was visually based upon the design of the John-O.88, a trawler launched in 1936. It sunk in 1941 after being attached by German fighter planes. Hergé had sketched this ship in Ostend docks before obtaining both detailed plans of the trawler from its builders, Jos Boel & Son, and a small-scale model from a collector.