The Watchtower-class of space stations were introduced in the 23rd century, typically taking four years and nine months to construct. They were considered a major base of operations within Starfleet and functioned as support for colonisation efforts amongst other projects. One such station was Starbase 47, also known as Vanguard, which was located in the Taurus Reach. Another such station was Starbase 6, which hosted the ill-fated M-5 computer simulation and war games. (VAN novel: Harbinger, TOS episode: "The Ultimate Computer")