Sorry for the title, it is not very evident and intuitive but I really do not how to tell it better...
Well, you know, several times, or better, many times, we use this form:
If I want to say:
"development of special weapons was the first point in Hitler's program..."
I will say this (a better form):
"special weapon development was..."
OK...
is it
"special weapon development"
or
"special weapons development" (note the plural...)
what's the grammar rule in order to understand how to use this very used form?