Factbox: The F-35 - stealthy, numerous and expensive

By Gerry Doyle (Reuters) - The F-35 Lightning II that crashed on Tuesday was one of a growing global fleet of advanced 'stealth' aircraft sold to U.S. allies, and the first to be assembled in Japan. There are already about twice as many copies of the F-35 flying as there are of its older brethren, the F-22 Raptor, and many times more than non-Western competitors such as the Russian Su-57 and China's J-31 and J-20. The plane is designed to be fast, but not the fastest; nimble, but not the most ni