In mid-January 1945, Kellex proposed an extension to K-25 to allow product enrichment of up to 85 percent. Grove initially approved this, but later canceled it in favor of a 540-stage side feed unit, which became known as K-27, which could process a slightly enriched product. This could then be fed into K-25 or the calutrons at the Y-12. Kellex estimated that using the enriched feed from K-27 could lift the output from K-25 from 35 to 60 percent uranium-235. Construction started at K-27 on 3April 1945, and was completed in December 1945. The construction work was expedited by making it "virtually a Chinese copy" of a section of K-25. By 31 December 1946, when the Manhattan Project ended, 110,048,961 man-hours of construction work had been performed at the K-25 site. The total cost, including that of K-27, was $479,589,999.