In 1941 the British used a GEE bombing system that utilized parabolic radar signals to navigate within 50-yards of a bomb-release point. When the Germans jammed GEE it was replaced by OBOE. OBOE allowed German night fighters to home in on the bombers. OBOE was accurate within 300 yards but had to be replaced by GH, which functioned so well that it was only used for special operations. GH had 90% accuracy regardless of weather.

H2S (H2X) was the British microwave radar that used a rotating parabolic antenna powered by a centimeter magnetron trans/receiver. This was similar to the U.S. APQ 13. This type of radar gives a map-like picture of the ground and is very useful for navigation. However, H2S could be easily tracked from the ground and used to vector German night fighters. LORAN for navigational purposes did not function well in Europe because of German jamming. LORAN in the Pacific worked well and was never jammed by the Japanese. LORAN over water had a 2% system error. Which at the 1400 miles from the Marianas to Japan amounted to only 28 miles.

The Germans were homing on IFF, H2S and jamming everything else. However, they did not use chaff or window. These were types of aluminum foil strips that would turn radar screens into masses of snow instead of returns. The British had window and chaff but were reluctant to use it for fear the Germans would learn to use it as well.

APQ 13
It is sometimes difficult for Americans to admit indebtedness to the English. Especially, if you were in the CBI. Without the British, radar as we knew it in

In 1939, the British rediscovered a fundamental electronic circuit. This circuit was first created by an American, Albert W. Hull, in 1916, while trying to circumvent a patent suit over the vacuum tube. The British scientific group took Hull's idea and made a magnetron. Yes, the same as is today used in a microwave oven. They created a radar transmitter tube three thousand times more powerful and useful than any other called the cavity magnetron.

In 1940, Winston Churchill delivered on his own, without other official knowledge or prior approval, about a dozen key inventions and the cavity magnetron to the United States. The magnetron was and is the heart of radar. Our navy did not start to win in the Pacific or Atlantic until aided by magnetron radar. By 1943 a blending of British and American scientific capabilities resulted in the best of both being incorporated into the APQ 13 airborne radar set. This was the standard navigational and bombing radar set used in

American airborne radar training began by flying in Lockheed 'Hudson' bombers equipped with the British 521 radar set. It has two large yagi antennae on the wings, one to transmit and the other to receive. The oscilloscope had a straight line and hair like projections would lift off the line to note a target. The size of the target showed by the number and size of the reflections. I was once the operator when I was asked to identify a large target. I could not. How many people have seen a blimp on a radar set?

The essentials of the APQ 13 are the transmitter, receiver, synchronizer, rotating parabolic antenna and the PPI (plan position indicator) scope. The bombing capability was an add-on that left much to be desired.

Most of us are familiar with the echo like qualities of radar. A pulse is triggered from the magnetron heart of the transmitter and sent through a tuned wave-guide to the antenna about every 200 microseconds. During the wait period a very small portion of the signal might be returned as an echo. Aircraft constructed to evade radar do so by having angled construction that reflects any radar pulse in a direction other than back to the sending antenna.

At the same time a five inch phosphorescent PPI tube would have an electron beam moving around and out synchronously with the antenna and the transmitted pulse. A very small portion of the transmitted pulse would return as an echo to the antenna and receiver. The echo would be shown as a bright spot on the PPI scope. Water generally does not show an echo. Land or ships bordered by water show clearly. Cities are somewhat brighter than land. Considerable experience and skill are required to tune, focus and interpret what appeared on the early scopes. (Today, computers enhance the raw echo into TV clarity.) A second scope was in the Navigators position for his use.

The addition of bombing capability made it possible for a calculated bomb release line to be superimposed on the PPI. A sector scan could move the antenna quickly over just the forward direction. This would allow the radar operator to adjust a target tracking arc to follow a discernible target. The major problem was that most targets were not easily identified by the radar operator. The built in circular error (bombing error) of the equipment left much to be desired.

Some figures indicate that, on average, the bombs dropped in

Navigation was a primary benefit of the APQ 13. It would show rivers, bays, islands, and such with considerable clarity. A comparison with a chart would greatly facilitate landfall recognition and assembly areas. The ability to navigate and locate by radar must have saved thousands of lives in

The APQ 13 was operationally rather complex. The transmitter and wave-guide to the antenna had to be maintained as a pressurized unit for proper operation. Its curvature and length functioned much as a tuned exhaust stack does. It was all too common to have this pressurization leak and fail at high altitudes. The parabolic antenna usually was mounted beneath the aircraft. It was contained in a plastic dome that could be lowered for best operation. The dome was held in place by many closely spaced screws. When the dome had to be removed reinstallation of these screws was very difficult. If one screw fell into the dome you had to take the dome off and start over. The power and waveform of the antenna could be checked by walking around a stopped antenna with a neon bulb. The APQ 13 had sufficient power to make the bulb light with radio frequency power for hundreds of feet from the antenna.

At the squadron level very little repair was done. Usually the components were removed and replaced with spares. Defective units were sent to the service squadrons for repair. The components of the APQ 13 were connected by numerous cables. No matter how carefully these cable connections might be made the effects of humidity, corrosion, and vibration could cause radar failure. In the event of failure the connections were the first thing checked. In an era of vacuum tubes the failure of any one of the thirty or forty tubes was more a probability than not on any given flight. A major difficulty seemed to lie in the inability to obtain a consistent regulated level of electrical power. This latter problem was made worse if operations were at high altitudes as they were in the China, Burma, India theater of war.

In the last few months of the war the APQ 13 had a new bombing computer attached and was then called the APQ 23. The APQ 23 had the same azimuth and tracking knobs as the Norden bomb sight. It was electronically synchronized to the bombsight and the bombardier could take over if visual bombing became possible. Digital read-outs were on the set, which would give ground speeds as well as time and distance to release point. In the days before digital computers all the resistors and taps from them were made trigonometrically. Such a wire wound trigonometric resistor was a work of art.

Lastly, the APQ 23 made possible offset bombing. A target, invisible to radar, could be preset as to distance and azimuth from a radar visible point. The bomb run would be made tracking a point easily seen on radar. The offset figures in the APQ 23 would drop the bombs on target. These abilities of the APQ 23 have arrived and are being used by aviation today in slightly different forms as distance measuring equipment (DME) and area navigation (RNAV).

I was a radar mechanic, Military Operation Specialty (MOS) 718, who came to India by way of North Africa at the same time as Pat O'Brien's USO Troupe. Fifty of us flew over at that time in small groups. We were divided among all the B-29 groups and squadrons. In early 1945 the B-29s were moved from India to Tinian and aircraft and electronic equipment performance improved dramatically.
Continued by writings on LORAN and the Supersonic Trainer.

Engine Knock
Engine knock was never effectively studied until high-speed cameras were able to photograph the ignition of fuels inside a cylinder. Full understanding of fuels was not achieved until the 1990's when even faster photographs became possible.

Knock and pre-ignition were once considered one and the same. In 1917 they were distinguished. Additives were used to control knock but costs and side effects were often prohibitive to future improvement. Finally in 1921 tetraethyl lead was found along with a bromide to give antiknock improvement without damage to the spark plugs. By 1930 octane rating had reached 87 at high power. To maintain a standard each fuel batch had to be blended and mixed according to the time of year and the source of the base oil. By 1934 100 octane fuel was being produced that gave a 30% increase in engine power with no increase in engine temperatures. This industrial prescience assured U.S. fuel dominance during

The fuels used by the Air Force over the objections of the War Department gave at least 20% more power, 6% more speed and 50% better climb speeds using existing engines. The Navy had made the transition by 1938. England was able, using U.S. 100 octane fuel, to get 1700 h.p. From the Merlin as opposed to 1000 h.p. previously. At the start of

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