Standard IFF (SCR-595 & 695) used a single quarter-wave dipole (about 14 inches long) usually mounted on the bottom of the airplane. Interrogator-responsors could trigger a response from standard IFF (and RACON) allowing these target’s positions to be displayed on the responsor’s CRT.
Earlier in the war, 58th Wing CBI B-29’s used SCR –729 to trigger BABS (Blind Approach Beacon System…. AN/CPN-7) as part of the SCS-51 ILS. With the move to the islands, this navigational need diminished and fewer Superforts were equipped with it. Most of those so equipped were typically intended for navigational or SUPER DUMBO rescue work. A triggered response from standard IFF that was squawking the emergency code was very wide, and left an unmistakable scope signature from returning ships that were likely to ditch, permitting a timely rescue.
Incidentally, the single forward antenna in the photo was the transmitting antenna, the larger array - receiving. Symmetrical mounting made the incoming triggered response directional. -Adrian
