>>845114 (last bread)
Another possible meaning of "owl" is Omni-Directional Weapon Locating Radar:
>The OWL is a next-generation radar technology that provides hemispherical coverage against indirect, low, non-standard trajectories and plunging threats.
www.cerdec.army.mil/inside_cerdec/i2wd/
(expand Radar section to see)
As a side note, Y-stations were British signals intelligence collection sites during WW2 (think Bletchley Park and Alan Turing). Could another meaning of Y-head be a code-breaker?