WRAITH,
Hence, to bring a craft into a turn from a straight flight requires action of force. The energy to generate that action of force must come from somewhere (energy is conserved), and that's from its kinetic energy of forward motion.
That's where you suggested otherwise. That part of what you said is not correct. A force can exist without consuming energy, for example the centripetal force in circular motion. There is a centripetal acceleration but at constant zero radial velocity and no change of radial displacement.
SAR bloke, read again what I said. Drag doesn't just act on the aircraft, its equal and opposite effect acts on the air. That's why a slipstream exists behind lorries. KE is taken out of the air that is decelerated from '300 kts' to a lower value by drag, in the example.
If you're hovering into a 25 kt wind with, say 8 deg nose down and you yaw the helo down wind maintaining your 8deg nose down, yes eventually you will be flying at 25kts AS, 50kts GS (ignoring stoofing into the ground due to loss of translational lift), but it will take time to reach that equilibrium. During that time you are experiencing a transient reduced airspeed. Same deal to a lesser extent in forward flight.