The odd-looking "Ontos" self-propelled recoilless rifle(s) was prized by the Marines in Vietnam for its agility and firepower. Designed to counter the threat of a massed Soviet armoured assault, the M50 Ontos showed its merit in the jungles and streets of Vietnam. Ontos grew out of Project Vista, the secret study of possible improvements to NATO defenses. Project Vista identified the need for an inexpensive, heavily armed "something" to thwart waves of Soviet armor. Armed with six powerful recoilless rifles, the diminutive M50 was given the name "Ontos," an Army mistranslation of Greek for "the Thing." Initially, the Army felt that the Allis-Chalmers T165E1 (later standardised as the M50) was the thing to fill the recommendation of Project Vista. Ultimately, and after some controversy, the Army lost interest in the vehicle, but the United States Marine Corps believed in the vehicle and in 1955 the M50 entered production. While the Corps first used the Ontos in Santo Domingo in 1965, it would rise to fame in Vietnam, where the M50, as well as the modernised M50A1, saw considerable use as antipersonnel weapons and in perimeter defense. On the streets of Hue, Marines made considerable use of the Ontos, blasting open walls and using antipersonnel rounds to create faux smoke screens. Over 270 photos, many in colour, chronicle the development, production, combat use, and details of this famed vehicle and the men who used them. AUTHOR: Since 1999, David Doyle has written over 200 published books, and the range of topics has expanded to include warships and combat aircraft. These books have ranged in size from 56 pages to large works approaching 1,000 pages. SELLING POINTS: . US Marine Corps lightweight, mobile tank killer with six M40 106 mm recoilless rifles . Used in Vietnam by the USMC for both jungle and urban warfare 270 colour and b/w photographs