The vehicle was originally introduced as the "Bobcat" which was owned by Moose Roberts so he and Tom Thomas could take wildlife photographs during their first outting Tom suggested it would be more appropriate as it was amphibious to call it the "Catfish" however their difficulty with handling it caused them to be swept out to sea which then they required rescuing. After being rescued, Tom & Moose call the vehicle diffrent names with Tom calling it the "Duck-Billed Platapus" and Moose calling it the "Natter Jack Toad".
During a hurricane it was used by Sam and Penny to race back to Pontypandy to help put out a fire at the fire station. By the end of the special Moose donated the vehicle to the fire service, newly painted in fire station colours and given blie lights and a Hi-Lo siren & re-named "Hydrus" by new Fireman Arnold McKinley. Hydrus is parked in the 4th Bay of the New Fire Station.
Being amphibious allows for it to be driven on both land and water.
Since being donated to the Fire Service, Sam has been the only one driving it, although Arnold has driven Hydrus in still images.
- Hydrus is based on the Max IV 6x6 Amphibious ATV.
- Hydrus is the first emergency vehicle since Venus in 2005 to obtain a real siren: a Wheelen Alpha Hi-Lo
Episodes Sam drove Hydrus
Episodes Moose drove Hydrus
- Everyone else in the fire station has yet to drive Hydrus.
- Hydrus cannot operate in the ocean as seen in Heroes of the Storm & referenced in Dog Day Disaster