They were disparaging referred to as “automatic rifles” because as everyone knows, a real machinegun is on a tripod and water cooled. Yes, they just replaced the battalion Vickers guns at first.
The legacy of the Machinegun Corps and is frantic attempts to carve out its own little empire was partly why in WW2, British infantry divisions had the rather bizarre concept of a divisional MG battalion. That, and the cost to a parsimonious Treasury of providing each battalion with its own MG Company.
"Mistakes in the initial deployment cannot be rectified" - Helmuth von Moltke