Why's that. o.c.? Do you think them a myth?4ft 6in one was my first rod, but there were longer multi piece ones - my mate had one. I don't think there were ever tank aerial fly rods.
There were certainly hollow steel rods made in the 50s & 60s (e.g. Accles & Pollock 'Apollos') and I've read references to tank aerials which may have been the layman's choice after the war for some home-builders. It seems feasible enough to me - though I doubt they were pleasant to cast!
I've also read that these long, metal tank aerials had a habit of catching powerlines and giving the crew of the tank an electric shock! To obviate this the aerials were covered in a hollow, tapering fibreglass sheath .....
Can't think how a fisherman might use that, though.