What are some of the inventions Leonardo da Vinci planned but didn't make it into the real world??????

His project on the idea of "walking on water"? All I know is that his invention called the Leonardo Tank didn't work so well when the British Army constructed it. I wished that I could help you but I borrowed my book on " Da Vinci Notebooks" to my friend a month ago...there's a chapter only on his inventions, maybe you can find that in the library. Sorry..