Amazon has filed a patent for yet another crazy idea to go along with its flying fulfillment centers and drone hives: underwater warehouses.

The patent calls for packages to be stored underwater in specialized tanks. The packages drop from the air, parachute down to the water and then sink to a specific water level based on density. When it is time for the package to leave, coded acoustic tones activate a balloon that fills with air from an attached cartridge. The package then floats to the surface for retrieval by drone or employee, depending on design.

The plan takes the idea further, detailing warehouse-like shelves underwater at different depths based on density.

The patent was filed last September with Jeremiah Brazeau of Amazon Robotics credited as the inventor. It gives clues as to what Amazon was thinking with the crazy idea. The online retailer hopes the new design will assuage some of the challenges experienced in its land-bound facilities. Amazon's traditional fulfillment centers are “increasingly large and complex facilities," the patent reads, with some workers being forced to walk miles per day in a 1M SF fulfillment center. Water offers unique storage advantages.

“The storage of items at various depths or heights within an aquatic storage facility may be particularly advantageous where the items are of different sizes or shapes, or where demand for such items may vary,” according to the patent application. It is much easier to go vertical in water than on land.

Amazon, like many large corporations, is sitting on hundreds of patents that will never see the light of day. Only time will tell if this idea sinks or swims.