Robert M. Gary wrote:

I had to fly IFR once before w/o the mode C (it broke in flight) but
this was the first time w/o any trasponder.

Back before 9-11 I got to fly a few times in the Washington Class B
with no transponder. To cap it off the IAD primary radar was out (i.e.,
if you didn't have a transponder, you were invisible to them).

Of course, these days you'd get shot at if you tried such a thing here.