The Mark 26 nuclear bomb was related to the
US Air Force, or AEC. As the decision not to pursue the "clean" Mk-21 closely coincided with the decision to terminate development of the Mk-26 in April 1957, it is possible that Mk-26 was the designation for the clean version of the Mk-21.
- Hansen, Chuck, "Swords of Armageddon: U.S. Nuclear Weapons Development since 1945" (CD-ROM & download available). PDF-2.67 Mb. 2,600 pages, Sunnyvale, California, Chucklea Publications, 1995, 2007. ISBN 978-0-9791915-0-3(2nd Ed.)