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.
Rensningsmetoderne, som til sidst blev anvendt i 231-W, var ikke kendt da byggeriet begyndte den 8. april, men fabrikken blev færdig og metoderne udvalgt ved årets slutning.