Feature Suggestion: Spy plane tech tree

[Sharpe_95]

As title really.

In my mind these could be used to penetrate into enemy territory to perform recee with a reduced range 'radar' (say equivalent to an early SAM in game- just enough to look at a specific spot or along a specific route.

Progression could be (somewhat anochonistcally):
- U2 (flies very high, but slow, can only be attacked by advanced SAM and advanced aircraft)

- Blackbird (flies very high and fast, can only be attacked by advanced SAMs and advanced aircraft with advanced air to air missiles - if they happen get close enough.

- Aurora (flies very very fast and high, cannot be attacked, except perhaps by ABM or advanced ABM units?).