You’re joking, but it’s predecessor was actually DEF-F. There aren’t many details but it’s some kind of electronic countermeasures/data collection system. See

You’re joking, but it’s predecessor was actually DEF-F. There aren’t many details but it’s some kind of electronic countermeasures/data collection system. See the museum exhibit here: http://www.sr71.us/sr_sensors_pg3.htm http://www.sr71.us/sr_sensors_pg3.htm