The smaller shuttlepods were introduced during the second season of Star Trek: The Next Generation to alleviate the costs associated with building exteriors and mock-ups of the larger, more elaborate types of warp-capable passenger shuttles. These ships were designed to carry fewer people, and had slower speeds. Originally intended by designers to be impulse-only, dramatic requirements often had the shuttles traveling long distances that would require warp speeds, and the type-18 has been explicitly stated to have warp drive. The type-15 were often specified as impulse only, so we must assume that when they were shown in use for long range travel they were fitted with a warp drive that was not previously part of its outfitting (we could likewise assume that impulse-only type-18s exist). Many shuttle designations and specifications were never spoken onscreen, but are derived from background graphics and artwork, and are reiterated by the Star Trek: The Next Generation Technical Manual and the Star Trek: Deep Space Nine Technical Manual.