Has there ever been a tail-dragger with retractable tail-gear? This comes from a slightly related question about drag from landing gear.

A tail-dragger is the old-school layout of aircraft, particularly WW2-era fighters. It's also known as Conventional Landing Gear.

The first two landing gear is usually retractable, but the tail wheel is not.

At least, I have never seen such a configuration with a retractable tail wheel. Has there ever been one?

Note: question excludes now more common tri-cycles.
Yes, there are. The Boeing B-17 FLying Fortress is one example of an aircraft designed with a retractable tailwheel.


Source: USAAF via Wikimedia, Public Domain (USGOV-PD)

Another example would be the Vought F4U Corsair:


Source: Wikimedia, cc-by-sa-2.0

Doubtless there are also other examples of aircraft similarly equipped with retractable tailwheels.