From Robert: "No, the United States did not pioneer the use of barrel bombs. Zionist militias used them in the 1940s. Irgun Zwai Leumi appears to have started it off, against the British. ("Terror out of Zion," p.245).
Then Haganah used them as an instrument of terror in its campaign to ethnically cleanse Palestine. See Chapter 7 of "The Case for Palestine: An International Law Perspective" (originally published in 1990 as "Palestine and Israel: A Challenge to Justice") p. 59:
When they attacked Arab towns, Haganah units used barrels filed with explosives, a device that had been developed by the Irgun.(32) As explained by Leo Heiman, a Haganah officer, they sent these barrel bombs "crashing into the walls and doorways of Arab houses" to encourage the residents to flee. The bombs "exploded with a furious sound like an erupting volcano, sending up sheets of flame and pillars of nauseating smoke." Then the Haganah personnel brought up jeeps with loudspeakers which broadcast tape-recorded horror sounds. "These included shrieks, wails, and anguished moans of Arab women, the wail of sirens and clang of fire-alarm bells, interrupted by a sepulchral voice calling out in Arabic: 'Save your souls, all ye faithful! Flee for your lives! The Jews are using poison gas and atomic weapons. Run for your lives in the name of Allah'"(33)
(32) R. D. Wilson, Cordon and Search: With 6th Airborne Division in Palestine (1949),
pp. 144–147.
(33) Leo Heiman, All's Fair . . .," Marine Corps Gazette (June 1964), p. 37, at p. 39."
Then Haganah used them as an instrument of terror in its campaign to ethnically cleanse Palestine. See Chapter 7 of "The Case for Palestine: An International Law Perspective" (originally published in 1990 as "Palestine and Israel: A Challenge to Justice") p. 59:
When they attacked Arab towns, Haganah units used barrels filed with explosives, a device that had been developed by the Irgun.(32) As explained by Leo Heiman, a Haganah officer, they sent these barrel bombs "crashing into the walls and doorways of Arab houses" to encourage the residents to flee. The bombs "exploded with a furious sound like an erupting volcano, sending up sheets of flame and pillars of nauseating smoke." Then the Haganah personnel brought up jeeps with loudspeakers which broadcast tape-recorded horror sounds. "These included shrieks, wails, and anguished moans of Arab women, the wail of sirens and clang of fire-alarm bells, interrupted by a sepulchral voice calling out in Arabic: 'Save your souls, all ye faithful! Flee for your lives! The Jews are using poison gas and atomic weapons. Run for your lives in the name of Allah'"(33)
(32) R. D. Wilson, Cordon and Search: With 6th Airborne Division in Palestine (1949),
pp. 144–147.
(33) Leo Heiman, All's Fair . . .," Marine Corps Gazette (June 1964), p. 37, at p. 39."
