Project Blue Book file, RB-47, July 17, 1957

Read from the scan by GLM-OCR; expect the odd misread word.

In the RB-47, the pilot and co-pilot sit in tandem in a bubble canopy so their conversations must necessarily be conducted via the airplane's interphone system. As Chase and co-pilot James H. McCoid began to speculate on what they had seen and the possibility that it might be a UFO, their conversation was heard by the Elint operators sitting within the RB-47 fuselage who had not been able to see the luminous object.

## THE THIRD INCIDENT:

When McClure noticed ECM Monitor #3, Walter A. Tuchscherer, laughing and asked the reason, Tuchscherer (who had been listening on the RB-47 intercom) replied: "They're chasing flying saucers up-front," according to McClure's recent recollection. This prompted McClure to think about the anomalous S-band signal he had earlier worked near Biloxi.

During the intervening time, McClure had re-tuned to work L-band radars in Louisiana and Arkansas. Now he decided to tune his APR-9 and ALA-6 back to S-band to see if he could find the earlier S-band signal. But it was not until 10:30Z, or 20 minutes after the visual sighting, that McClure detected an S-band signal, according to the Piwetz account. (This time figure and subsequent ones were hastily jotted down by McClure on scraps of paper, he recently told me.) It was only after this second encounter with an S-band signal, after 10:30Z, that McClure jotted down the characteristics of the signal:

Frequency: 2,995-3,000 mc.; Pulse repetition frequency (PRF): 600 per second; Pulse Length: 2 microseconds; Scan rate: 4 rpm.

The CPS-6B radar, an early post-war design, radiates six separate beams from three different antenna dishes. Each beam operates in a different part of S-band. The frequency and other signal characteristics noted by McClure are identical to those for the VERTICAL-CENTER BEAM -- except for the pulse duration/length at a PRF of 600/sec. According to the Handbook of Operating Instructions for the CPS-6B [T.O. 31PG-2CPS6-11, revised 15 Jan. 1957], when the radar is operating at a PRF of 600/sec., the pulse length is 1 microsec., not the 2 microsec. noted by McClure. But an Elint specialist who is familiar with the APR-9 Elint receiver says that smearing of the received pulse due to ground reflection could easily cause an operator to err by this small increment.

The newly acquired S-band signal, at 10:30Z, showed a bearing of roughly $ 7 0^{\circ} $ . This was roughly the same relative bearing at which the bright luminous object had zoomed out of sight some 20 minutes earlier as it headed north. IF this S-band signal came from the UFO, then the UFO must suddenly have changed course and was now flying abeam of the RB-47, somewhere out there in the darkness. However, the flight crew did NOT see any visual target at 10:30Z -- at a $ 7 0^{\circ} $ bearing or elsewhere.

One of the curious aspects of this incident is why the S-band signal did not show up on the ALA-6 until 20 minutes after the initial visual sighting. McClure assures me that it would not take more than 10-15 seconds for him to re-tune from L-band to S-band.

This delay is readily explained IF the signal detected by McClure at 10:30Z came from an FPS-10 radar (with signal identical to a CPS-6B) situated at Duncanville, just southwest of Dallas. Analysis of the RB-47's flight path and the coverage of the Duncanville radar's Vertical-Center beam at the RB-47's 34,500 ft. altitude shows that this beam's lower sidelobe would first begin to illuminate the aircraft at approximately 10:30Z. (See Fig. 6; also Appendix.)