A system fabricating composite preforms includes a layer assembly stage with a first stage for receiving new layers, such as layer N; and a second stage for holding up to K layers, such as layers N−1 to N−K. An interlayer reinforcement insertion mechanism inserts interlayer reinforcements Q through layer N and the layers N−1 to N−K, using a first layer spacing between layer N−K and layer N-K−1 in a completed layer stage. Following the interlayer reinforcements Q insertion, the layer assembly stage transfers the layer N−K to the completed layer stage; closes the first layer spacing, bringing layers N−K and N−K−1 into contact; and transfers the layer N to the second stage. The system repeats this cycle of receiving new layers, inserting interlayer reinforcements using layer spacings between the second and completed layer stages, closing these layer spacings, and transferring layers to construct composite preforms with arbitrary numbers of layers.