Early Spitfires like the I/II/V had the aerials (IFF) on either side of the fuselage attached to the stabalizers.
When the VHF radio sets came out, these were omitted and they now had only one aerial running from the mast to the top of the rudder on some occasions.
Spitfires with wider-chord rudders were different. If you look at our Spitfire VIII's strbrd wing carefully, you'll notice the little antenna sticking out from beneath. That's the new IFF aerial.