In March 1948, the Air Force decided that both the F-84 and F-86 would be equipped with the newest version of the A-1 sight, the B model, which was considered to be the most accurate lead computing sight available to the Air Forces. (29) Its radar set could lock-on a target at 5,400 feet range. The pilot then checked visually to ensure that he was locked on to the proper target (if not, he pressed a target rejection switch and maneuvered until the radar locked onto the target desired) and “caged” the sight’s gyros by pressing a button on the control stick grip. After placing the reticle dot on the target and releasing the caging button, the pilot had to keep the reticle on target for one-half to one second (the time needed by the sight to solve the ballistic problem) before opening fire in one-second bursts. (30)
Due to ground clutter, manual range was utilized when either the radar was inoperative or the aircraft was below 5,000 feet. Manual ranging was stadiametrically set by entering the target’s wingspan on the sight head target span wheel and rotating the range control on the throttle grip until the reticle contracted to its minimum diameter. As in radar ranging, the pilot pressed the electrical caging button and maneuvered the aircraft so that the reticle dot–called the pipper–was on target. He established a smooth track and, when the target’s wingspan filled the ranging circle, uncaged the gyros, waited a split second (one solution time), and began firing. If the computing or radar circuits of the sight were inoperative, the pilot could cage the sight mechanically with a lever on the sight head and use the fixed reticle for rule-of-thumb gunnery. (31)
During the fall of 1948, preliminary firing tests in F-84 and F-86 aircraft, revealed a problem that persisted throughout the life of the A-1 sight program–reticule jitter. Whenever the pilot pressed the firing button, the vibration of the guns either drove the sight reticle entirely from view or caused it to oscillate so rapidly that it became an orange blur. (32)
Flight tests to determine the best method of reducing reticle vibration to an acceptable level began at Muroc [later Edwards] AFB, California, in January 1949. The Sperry Gyroscope Company, which had been contracted to manufacture the first ninety-four A-1B sights, came up with a “fix” consisting of stainless steel stiffeners for the sight head mounting brackets. This reduced vibration considerably, but did not totally cure the problem.
That April, Sperry Gyroscope and the AC Spark Plug Company, which also built the A-1B sight, both agreed to produce 551 A-1C sights, with improved computing features, for the F-86A, F-86D, and F-94 aircraft. Full-scale production was scheduled to begin in August 1950, but the Air Force suspended deliveries of all A-1C sights until some method was found to make the sights more usable in the field. After a short period of review, the Air Materiel Command (AMC) authorized Sperry to modify thirty-five A-1C sights by providing a more efficient sight head and computer heating system, a brighter reticle, and special stiffeners to reduce reticle vibrations. The result was designated as the A-1C(M). After the modifications proved successful, the Air Force ordered that all A1 sights in the field be returned for conversion to the new configuration. By then, several different combinations of the gunsight and its radar had been installed in various versions of the F-86A Sabre coming off the production line at North American Aviation. (33)
The A-1B gunsights, with the AN/APG-5C radar, were provided as factory installed equipment beginning with the third production run of 333 F-86A’s starting with aircraft serial number 49-007. All earlier production versions of the aircraft had been equipped with the K-18 sight. The last twenty-four aircraft of this production run were equipped with the A-1C(M) gunsight, coupled to an improved ranging radar, the General Electric built AN/APG-30 installed in the nose above the intake. (34) The A-1C(M) sight and the AN/APG-30 ranging radar were to be retrofitted to earlier models in field installations. Radar production of the APG-30 manufactured by General Electric was inadequate to meet all of the service needs, however. Thus by the end of the Korean conflict, a considerable number of F-86As still contained older fire control equipment; some had A-1B or A-1C sights plus APG-5C ranging radars or earlier versions of the APG-30. (35)
The A-1C(M) Takes on the MiG–15
The first Sabres to arrive in Korea were the F-86A models, equipped with K-18 sights. These sights were soon found to be unsuited for the high-speed combat that ensued when MiG-15s were engaged. The K-18 was a modified version of the K14 gyro gunsight developed during World War II. Unlike the A-1C(M), it was dependent upon manual range control that was much too stiff and erratic. (36) Tracking at the high indicated air speeds encountered in Korea was difficult with the K-18: excessive movement of the reticle occurred when guns were fired, and a boresight speed of 357 knots made the sight useless when the enemy was pursued at indicated speeds of over 500 knots.
Most aviation historians of the air war in Korea agree that the A-1C sights were far superior to those on the MiG-15 and gave the American pilots a great advantage–when it worked. Although the A-1C and its radar differed radically from the gunsights it superseded, spare parts, spare components, and test equipment did not reach the Far East until mid-1951. (37) Both gunsight and radar were beset with a multitude of maintenance problems, some due to rough runways, which jarred delicate electronic components, but even more to a dearth of trained personnel and the necessary test equipment to keep the system operational. Keeping the radar operational proved particularly daunting. It did not take long for maintenance personnel to discover that once an electronic component failed the entire radar had to be replaced not just the faulty module. (38) There were other problems with the radar too. It performed erratically in clouds (due to moisture), sometimes would break radar lock, and would not work below 6,000 feet due to ground clutter. (39) All of the above, combined with a general lack of pilot training in the proper use of the sight, soon led many of the Sabre pilots to become disenchanted with the A-1C sight. As a result, many of them favored the clearly inferior, but dependable, K-18 sight, which continued in general use until the arrival of the F-86E, beginning in June 1951. (40) Others caged the A-1C’s gyro to eliminate radar and gyro inputs, turning it into a fixed gun sight. (41) The problems with the A1C sight proliferated until the director of operations for the Fifth Air Force declared it was “too complicated to be maintained.” (42)
Gen. Otto P. Weyland, commander of the Far East Air Forces (FEAF), felt that the A-1C(M) had not received a fair trial. At his request, AMC initiated an all-out remedial program (named Project Jaybird) to fix the problem. In April 1952, a team of personnel from the AMC and the Air Training Command (ATC), together with civilian technical representatives, arrived in Korea to resolve the supply and maintenance issues and to upgrade all A-1C sighting control systems (now designated as the J-1 fire control system) to the latest configuration. By the end of June 1952, the AMC team completed its work and ATC had begun to turn out the technicians needed to maintain the gunsight and its radar. (43)
The A-1C(M) sight had been designed to automatically compute lead at ranges up to 1,500 yards. The excessive “time of flight” required for the sight’s computer to provide a ballistic solution at this relatively long range caused the sight to be more sensitive to aircraft motion at longer ranges. Because of this, inexperienced pilots found it difficult to keep the pipper on the target as they tried to maneuver closer to a highly evasive MiG-15. This led to the development of the Jenkins Range Limiter. The limiter consisted of a range selector switch and a sensing device that prevented the radar range signal from exceeding the value selected by the pilot. This selector switch allowed the pilot to select his maximum desirable firing range before initiating the attack. When the radar indicated a range in excess of the selected value, the selected value was fed to the computer limiting the time of flight input so that the sight was less sensitive. When the radar range equaled or was less than the selected range, the radar value was fed to the computer. A change in reticle configuration simultaneously occurred, indicating to the pilot that he had reached the range selected to begin firing.
