"I suspect that's another Uban Legend."
It's not. At the Battle of Mons in August 1914 British units faced the German First Army in what was supposed to be a holding action.
Although heavily outnumbering the British, the German units were stopped dead by what they thought was massed machine gun fire.
In truth, I believe the British fielded only 2 machine guns (both in defensive positions at crossings over the canal) at the Battle of Mons; everything else was accurate rapid rifle fire.
The volume of fire was so heavy (not to mention accurate) that German Gen. von Kluck reported to his superiors that his troops were facing at least 2 battalions of British machine guns (in the German army at the time that would have been at least 24 machine guns).
In truth, at the time, the British only fielded 2 machine guns per battalion, a far cry from German TOE at the time (IIRC 12 machine guns per battion).
"And you never hear or a US Unit having the same rep despite having been all M1 equipped during the war (though the tong noise lives on, as if anyone could hear anything like that with their deaf ears)"
That's because the very nature of ground warfare had changed dramatically by the time the the M1 entered World War II.
Massed unit formations of the kind that were used in the early stages of World War I (and which the Germans used in their initial assaults against the British at Mons) were largely a thing of the past by the time the M1 entered service.
Edit in -- Another fundamental change had occurred to just about every military by the time the M1 entered service -- the rifleman was no longer considered to be the primary source of unit fire.
Machine guns were now light enough and mobile enough that they were deeply embedded at the company level.
In 1942, a US infantry battalion comprised about 900 men and had approximately 26 heavy (.50 and water cooled .30) and light (air cooled .30) machine guns, PLUS a significantly greater number of Browning Automatic Rifles (I think roughly 50).
http://militaryhistoryvisualized.com/us-army-infantry-battalion-structure-attack-tactics-1944/
and
http://www.hardscrabblefarm.com/images/ww2/infantry_rifle_org.gif