The designs are then prototyped using an in-house stereolithography machine. The patent was issued in the U.S. and the system was not prototyped or commercialized. The HLA specification was prototyped and refined, until HLA 1.3 was finally released. Fort Hancock was one of the first forts built and prototyped several weapon installations. A multiplayer networked version for the IBM PC was prototyped, but never released. From these proposals, design solutions are prototyped and then tested with the target user group. User-defined functions may be created at any time without being prototyped. Such a kernel contains architectural components prototyped in the Fluke operating system. Volkswagen had prototyped a notchback sedan version of the 411, without introducing it to production. Further technical developments were prototyped in , but the design was not continued. An OHV version was prototyped, but never produced. The earliest known design, was prototyped at a Boston-based sound reinforcement company in 1976. The Factor e Farm is the headquarters where the machines are prototyped and tested. A heat engine based on the Leidenfrost effect has been prototyped. A Sergeant Bash pitstop kit was prototyped but never released.