Yep. Heavy machine guns they are. What they did not say was that two of the heavy machine guns pictured are actually hand-carried Bofors 40 mm pom-pom guns.
Bofor 40 mm cannon
https://en.wikipedia.org/wiki/File:Bofors-p004596.jpg
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My father was an Armourer during WWII. He worked on Quad 50’s and Bofors. Some of the Bofors were anti-tank weapons.
Here is Bubba with a 20mm Lahti Anti-Tank Rifle
http://www.thegunzone.com/people/images/lahti.jpg
here is the 20mm ammo
http://www.thegunzone.com/people/images/lahti-ammo.jpg
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Source
http://www.thegunzone.com/people/lahti.html