New military systems are usually first acquired in low-rate production. This is a build rate that is slower than the eventual 'normal' rate of production, and is done for a few reasons. First, the first few whatevers produced (let's say aircraft) will usually display one or more medium-to-major faults or flaws of design or manufacture that need to be corrected, either through redesign or retooling. This ideally would happen as soon as possible in terms of the number of aircraft built, to save the cost of modifying earlier aircraft later on. In extreme cases, modification of finished units isn't possible. Second, low-rate production is a period for the manufacturer to iron out any kinks in the building process, including supply pipelines, assembly, etc.