During World War II bicycles were widely used by the various military forces, but because of rubber shortages various solutions were considered as alternatives when the tires went flat. The Japanese simply gave up the rubber and its soldiers rode their bikes on the rims.
Energy Return Wheel likely has a far better solution, one that could be quite revolutionary. It is developing an airless mountain bike tire that would use rubber or alloy structures in place of air chamber. This could provide a bounce effect that could even increase acceleration.
There might be some drawbacks to address, such as how to keep mud, rocks and other debris from entering the inside of the tire, but this could be a great way to ensure that you won’t get a flat tire on the trails!