Colonel Thomas X. Hammes is a retired U.S. Marine officer who is considered a specialist in counter-insurgency warfare. Hammes' first paper on fourth generation warfare appeared in the Marine Corps Gazette in 1994; he developed a book-length treatment while a senior Marine fellow in the Institute for National Security Studies at the National Defense University. In this work, The Sling and The Stone: On War in the 21st Century, he openly criticized The Pentagon and the Joint Chiefs of Staff. Both Hammes and William Lind make use of the term "fourth generation warfare", however Hammes considers it more of a "framework for study" rather than a revolutionary concept. Hammes traces the origins of fourth generation warfare to Mao Zedong.