Thanks for your response!
No menu appears at lower center of screen as it does for all other research. The only thing I get is that after hovering over the MARINES "button", a paragraph explaining MARINES appears.
I have now done all tier 1 research except MARINES so it seems that is bugged out somehow. Sadly it seems that other land units (except logistics) is dependent on MARINES...so I am outta luck for tier 2 troops.😞