Birdwatcher

Birdwatcher was a monitoring system unique to the A‑12. It utilized a multiplexed High Frequency, Single SideBand (HF/SSB) radio system and was designed to telemeter signals concerning the operation/non‑operation of various aircraft systems down to a specially equipped ground station. The frequencies selected for any particular mission were briefed and noted by the pilot on hand‑cards; they were also annotated on the mission filmstrip, which was displayed to the pilot in the cockpit. The system consisted of two main elements: an air element and a ground element. The air element was a subset of the aircraft’s HF/SSB radio, the antenna consisting of a tube structure within the aircraft’s pitot/static system located at the front of the aircraft. The relatively short antenna was closely matched to the ground plane, furnished by the airframe, and made a fairy efficient antenna. Of its 40 channels, 32 were used to monitor individual aircraft systems; for example, channel 54 covered the starboard engine’s EGT; channel 7, the starboard engine’s fuel flow; while channel 3 covered the aircraft’s altitude. If any pre‑set parameters of the systems being monitored were breached, Birdwatcher keyed and modulated the HF transmitter with a coded signal consisting of three consecutive half‑second bursts, each separated by a five‑second period of silence. During each of the half‑second bursts, the aircraft’s identity and the condition of each of the systems being monitored was transmitted. These three bursts could be heard through the pilot’s headphones as three chirps – hence the name Birdwatcher.

The forward and aft scanning heads of the Type I camera provided a level of stereo overlap directly below the aircraft before each then scanned out to the left and right, 67 degrees either side of the Oxcart’s track. (CIA Pilots Manual)

The A‑12 pilot had only limited control over the system. In the cockpit there were two switches; these were labeled “A” and “B.” The “A” code was usually used by the pilot to signify to the ground station that the aircraft had reached a pre‑designated point in the mission and that it was in a “GO” condition, such as at the end of a successful air refueling, or upon reaching a predetermined distance‑to‑go point or turn point. The pilot activated the “B” code usually to indicate that the aircraft had experienced some sort of abort condition. The two buttons could be used sequentially to indicate that something unusual had occurred; for example, “B” followed by “A” might be interpreted as meaning that the aircraft had an abort condition, but was not in an emergency situation. Involuntary Birdwatcher codes were transmitted automatically by the system when any one of a number of sensors tripped the encoder. All radio emitters on the A‑12 could be inhibited by the pilot by activating a “Mute” switch – except the Birdwatcher. The Mute system was installed on the aircraft to prevent accidental transmissions by a device such as the Tacan, UHF radio, etc. The pilot was usually instructed to operate the Mute switch by the mission filmstrip prior to entering denied territory.

Birdwatcher could also be interrogated by appropriately equipped ground stations. The Command Post (CP) could, if required, cause Birdwatcher to transmit a short burst of information that would include only the coded identification of the Oxcart – if no other sensors had already tripped. To the dismay of a couple of pilots, some of those monitoring the aircraft’s progress from the ground station at Kadena AB occasionally interrogated the aircraft when it was over enemy territory!

The ground station for Birdwatcher at Area 51 was located just outside the entrance to the CP, in the Secure Communications Room – a highly restricted area. From here, an operator monitored the Birdwatcher decoder using an oscillograph‑paper recorder upon which was recorded the Birdwatcher’s “chirping.” Lights were then used to develop the oscillograph paper to a point where it was possible that the technician could place the paper on a readout cursor and see which sensor had tripped. He then activated a switch that illuminated an appropriate light on a light board located in the CP, thereby alerting other officers as to the aircraft’s status.

ELINT

The A‑12 was also equipped with an electronic intelligence (ELINT) capability, known as System 6. This wide‑band collection system comprised a miniaturizing wide‑frequency receiver which monitored C, L, X, and P bands. These were then split and recorded by two three‑channel recorders working at 2¼ inches per second; C and X band information, together with capture time and left or right of track directional information, was channeled to one recorder, whilst the same data for L and P bands was stored by the other unit.

Parked up on the north ramp, an early shot during the Oxcart test program reveals seven A‑12s, the AT‑12 trainer, and at the far end two YF‑12A interceptors. (Lockheed Martin)

ECM

All systems were activated by a single, three‑position power switch labeled OFF, Standby, and ON. There was also a built‑in‑test (BIT) switch that activated a logic test to ensure that each element worked correctly. These checks were undertaken by the pilot prior to entering denied territory; satisfactory completion of the checks caused the Birdwatcher to chirp, which confirmed to the ground station that the aircraft was about to penetrate hostile airspace. If the BIT check failed, it was mandatory for the pilot to abort the mission – in God and ECM we trust!

The only elements of the system that were visible to the pilot were a series of five lights positioned above the view scope and enclosed in the cockpit glare shield. The outboard lights were marked DF, the set inboard of these were marked LI, and the larger center light was known as the JAM GREEN or JAM RED light. The DF lights illuminated when the ECM system detected that a SAM target acquisition system was tracking the Oxcart. If only one of these two lights were on, it indicated the general direction of the tracking radar; if both were on it meant that the SAM system was either ahead or on both sides of the flight path. The LI lights illuminated when the SAM site’s radar had gone into a high PRF (pulse repetition frequency) mode and usually indicated that the SAM site had actually launched one or more missiles. Frank Murray recalls the usual sequence of events:

When a SAM site was on you, the DF light or lights would come on and this started the Birdwatcher chirping. Then the LI light[s] would come on, indicating a missile launch. Then came the moment of truth! Sometime into the missile flight‑time, the active parts of the ECM suite would activate and the JAM GREEN light would illuminate. This indicated to the pilot that the ECM system was working to counter the missile’s guidance system. If however the JAM RED light illuminated, this indicated that the active elements of the system weren’t working correctly, in which case the pilot then had to depress and hold‑down a button marked JAM O’RIDE [JO], located on the top‑right portion of the flight control stick. This activated the noise‑jammer part of the ECM suite – I have to say though, that I’m not aware of anyone in the program having to use the JO button.

The various elements of the ECM suite were given cryptic names. Pin Peg was a radar homing and warning (RHAW) receiver, and monitored S‑ and C‑band frequencies to indicate the presence and approximate position of Fan Song SA‑2 target acquisition radars; if required, it also activated the jammer. Blue Dog II was the hardware that provided Oxcart with the protective element of the ECM suite. It was a large deceptive radar countermeasure system weighing in at 480lb, and required power output of 20kW and antenna gain greater than 79dBm. Utilizing a technique known as range gate pull‑off, it deceived the SA‑2’s missile guidance system by generating false guidance commands. Pin Peg and Blue Dog II were used in association with either Big Blast or Mad Moth. Big Blast also covered both S and C bands, generating, when required, barrage and deceptive noise protection against SA‑2s; Mad Moth provided protection in S and C bands against SA‑2s by using angle deception.