155mm Howitzers, the Most Firing Power for the Marines

On D-Day+11, US Marines fire heavy artillery on Iwo Jima:

155MM HOWITZERS were the heaviest artillery available to Marines at Iwo. In general support of the corps, these weapons fired a total of 43,795 rounds. Most of this ammunition was expended in counterbattery and preparatory fire missions.

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Credits

US Navy photo, from Iwo Jima:  Amphibious Epic, United States Marine Corps Historical Monograph, by Lt. Col. Whitman S. Bartley, USMC.

Image located in Chapter VII - "5th Division on the Left (D+6 - D+19)," at page 134.