Yep,, SLA Marshall and his book "Men Against Fire".
Quote: In an average experienced infantry company in an average day's action, the number engaging with any and all weapons was approximately 15 per cent of the total strength. In the most aggressive companies, under the most intense local pressure, the figure rarely rose above 25 percent of the total strength from the opening to the close of the action.
End Quote
FORTY-ONE YEARS LATER...
"Marshall's ratio of fire...appears to have been an invention."
”” Roger J. Spiller, 1988