Western intelligence services had highlighted the air intake of "Fencer-B" b-n 21 (left) to focus on the lack of RWR antennas - that was not the case for 
b-n 39 (right). The latter was a "Fencer-C" for NATO because it had antennas for the SPO-15S <em>Bereza</em>
RHWR on the air intake and the vertical tail.