The purification methods that were eventually used in 231-W were still unknown when construction commenced on 8 April 1944, but the plant was complete and the methods were selected by the end of the year.
Os métodos de purificación que se utilizarían eventualmente no 231-W aínda eran descoñecidos cando a construción do mesmo comezou o 8 de abril de 1944, mais a planta completouse a finais dese mesmo ano cos métodos xa seleccionados.