Christopher Chant (2013-10-18). "Isabella". The Encyclopedia of Codenames of World War II. Routledge. p. 354. ISBN978-1-134-64787-3.
Christopher Chant (2013-10-18). "Isabella". The Encyclopedia of Codenames of World War II. Routledge. p. 354. ISBN978-1-134-64787-3.
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Gerard F. Rutan (1970). "Hitler's Frustrated Conquest". University of Portland Review. 22. Portland: University of Portland: 3—17. ISSN0041-9923. OCLC655675137.