From the Super Mario Wiki, the Mario encyclopedia
Steerable Barrels (also referred to as Steer Barrels in an issue of Nintendo Power) are a type of Barrel Cannon that only appears in Donkey Kong Country 2: Diddy's Kong Quest. They only appear in Fiery Furnace, where they have a crucial role of carrying Diddy and Dixie Kong across the enormous lava gaps. Steerable Barrels are recognizable from a control pad depicted on on them.
When Diddy and Dixie enter the Steerable Barrel, they are able to move it around in any direction freely. However, unlike Rotatable Barrels, the Kongs cannot rotate and aim the barrel because it always faces one direction. Most Steerable Barrels have a timer when entered, and it varies from 1–5 seconds. When the timer reaches zero, the Kongs are automatically blasted out of the Steerable Barrel, which also vanishes and returns to its original location. This means Diddy and Dixie must quickly blast into the next Steerable Barrel or fall onto the nearest land.