***PC; Do you know the designation for this particular heavy duty Zippo?
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Looks to be a M777, 155mm (just over 6 inch) howitzer - used by the US Army and USMC (and about a half-dozen other countries).
Video of the M777 through Night Vision Googles (NVGs)
https://www.youtube.com/watch?v=a5ns8MYfkE8 (just over a minute)
https://www.youtube.com/watch?v=CdO_0twP_CU
A good gun crew is poetry in motion - 15 rounds in under 3 minutes (fun starts at about 1:30 and there is some language...). Remember that each projectile weighs about 95-100lbs...