Two fish are in a tank. One turns to the other and says, "How do you drive this thing?"
Why this joke works
Let the Tank Change Shape
The opening naturally places two fish inside an aquarium. The question forces “tank” to change into a vehicle that needs a driver, creating a new and absurd picture without changing any earlier words. Keep the setup short and ordinary. Pause after the first sentence so the aquarium image settles, then give the fish's question with sincere confusion rather than a comic voice. The cleaner the delivery, the faster listeners can replace the glass fish tank with the armored kind in their imagination.
A closer look
One Container Silently Changes Into an Armored Vehicle
The opening picture is completely ordinary if “tank” means an aquarium. The request to drive it forces a second reading: the fish believe they occupy a military vehicle. Having only one fish speak makes the other an equally unqualified crew member. The joke ends at the question, letting listeners build the controls, confusion, and underwater vehicle scene without an explanatory punchline.
Fact behind the joke
Fish Tanks Require Active Water-Quality Management
NOAA aquaculture guidance notes that decomposition of algae, bacteria, and fish waste consumes dissolved oxygen, while excessive ammonia production can create problems in recirculating systems. Tank health therefore depends on stocking, filtration, aeration, temperature, feeding, and monitoring. An aquarium is not merely a glass container full of water, though it remains considerably easier for fish to inhabit than an armored vehicle with controls.