Turn turtle
Definition 1 of 2
Pro Tip 1/3Nautical Origin
Originating from sailing, where 'turtle' refers to a boat flipping like a turtle shell. 
After being hit by a rogue wave, their boat turned turtle.
Pro Tip 2/3Complete Overturn
Emphasizes a complete flip, meaning the underside becomes the top. 
During the storm, we watched in horror as the caravan turned turtle.
Pro Tip 3/3Sudden Event
Indicates an abrupt incident, often accidental and surprising. 
I swerved to avoid the dog, and the car nearly turned turtle.