As a former navigator, this is an interesting little story… I’ve seen and used a driftmeter before, and when I retired, we were using prototype GPS units…
A crucial part of flying is the ability to navigate, absent this flight is dangerous. In aviation’s early years, life-saving instruments were either crude or nonexistent. The lack of navigation equipment was the principal reason for the 32 men, out of 230 men, who lost their lives flying mail for the Post Office Department between 1918 and 1927. The lack of navigation equipment made flying mail for the Post Office Department just as dangerous as flying over the trenches during World War I.
Prior to WW II, flying on instruments relied on dead reckoning making estimations of time-spent flying using basic questionable compass and primitive maps readings. Early instrumentation was primitive, altimeters weren’t accurate, if they worked at all. The reasons being for this was that when flying in heavy fog or other vision obscuring conditions with no natural horizon for perspective, pilots quickly became disoriented, resulting with pilots flying into the ground while believing they were flying a safe altitude. Today navigating by visual reference to landmarks and dead reckoning are the primary tools used by pilots of recreational aircraft. In the days, leading up to World War II all pilots used this method, simply because there was nothing else to rely on.
B-29’s relied on Mount Fuji to be an ideal navigational waypoint for bombing missions into Japan, being the highest mountain in Japan, rising to 12,388 feet near the Pacific Ocean coast in Yamanashi and Shizuoka ken (prefectures) of central Honshu, about 60 miles west of the Tokyo-Yokohama metropolitan area, and can be seen from the city on a clear day. B-29’s were required to use dead reckoning navigation over the ocean, and land when forward based in China, and the Marianna’s, and this worked as long as the navigators use of their Astrodomes was not obscured by clouds, which limited the ability to track the sun, stars, and land navigational waypoints.
The B-29’s were designed with a radical navigational innovation being the Automatic Position Indicator produced by The Eclipse-Pioneer Division of Bendix Aviation Corporation. This was a navigator’s companion to the autopilot, and for the first time in aviation or marine history, a device could provide continuous readings of latitude and longitude regardless of speed or drift.
The brain of the API was a self-contained device, mounted on the instrument panel, and automatically performed all of the computing, calculating, and indicating functions. It instantaneously made calculations, which would have required the navigator to work for hours with charts, basic navigational reference books, star-sighting sextants, a chronometer, and parallel rules and dividers to calculate the position of the aircraft in flight. This system used a remote indicating earth induction compass and consisted of four main parts:
· A fluxgate which was a transmitter, a horizon gyro, an amplifier, and a master compass located in the navigators position.
· The fluxgate measured the directive force of the earth’s magnetic field determining the aircraft’s position relative to the azimuth relation of the flux gate to the earth’s directive magnetic force.
· As the aircraft would change direction, the angular relation of the fluxgate to the earth’s magnetic field was altered and this would provide new navigation data.[ii]
Two indicating counters, set in an instrument panel compass dial, indicated degrees of latitude and longitude and gave the navigator an exact and continuous reading of his position. This same dial also gave the navigator a distance measuring (DME) continuous record of nautical air miles flown, radio ranging, and indicated the correct compass heading of the aircraft. From these readings plus a check of the drift meter, the navigator could pin point his position immediately on the map.
Several problems were encountered with the API instrument itself.
· The problems were that the navigation computer failed to operate properly because of failures of the air mileage unit to transfer its power to the computer due to a shearing of the shaft from the gear to which it was attached in the pump units.
· The system was designed to work with a west to east calibration for a European Theater, and it required a North South recalibration to bomb from the Marianna’s.
· This caused the computer to fail to follow the compass in one direction.
· This caused the latitude and longitude readings to be in error while the compass read correctly.
· The recommended solution was for specially trained personnel to calibrate, maintain and repair the API.
· In a letter to the Commanding General of the AAF dated February 22, 1944, the 20th Bomber Command recommended that four “compass adjusters” be assigned to each engineering squadron of the service group, special, by addition to the Table of Organization.
· It was suggested that these “compass adjusters” should be specially trained in the maintenance and repair of the API. By May 26, 1944, problems with the API system were still unsolved when four API units had failed. The approximate flying time was 50 hours and all API use was discontinued on this date. By June 26, 1944, no reply was received by the 20th BC headquarters on any action by the ATSC to fulfill the requirement for “compass adjusters”. By December 27, 1944, about 70% of the API equipment was still inoperable because of a complete lack of spares for fluxgate and API units.
The majority of API units had arrived in theater with broken vacuum tubes, and other physical damages, rendering them inoperable. The majority of the navigation personnel stressed the desirability of having this equipment during individual flights such as photoreconnaissance flights and for formation leaders on bombing missions, in view of the absence of checkpoints in the broad Pacific. Wartime shortages left only one Pioneer technical representative available in the CBI Theater.
· It was considered imperative that at least one additional representative be made available to the 73rd Bomber Wing as well as additional trained ground personnel since the training of the ground echelons on this equipment had been inadequate.
· The training of the navigators in the use of the API and in the accomplishment of minor maintenance, such as the location and installation of the fuses, needed to be improved.
· Each airplane needed three each of the compass and repeater units installed in it.
· The only reason that any of the equipment was still in operation was that the technical representative brought along spares.
The failure to solve the problems with the API would negate the value this innovation would contribute to B-29 operations.
· The global Army Airways Communications System (AACS) would eventually provide radio ranging, and weather reports, for air traffic navigation.
· Radio ranging worked through Loran allowing a navigator to determine his position through the time displacement between radio signals from two known radio stations.
· By December of 1944, the AACS system had begun to expand to cover all Pacific Allied areas of operation, to include Japan by late in the war.
The impact of this was that the B-29 attacks on Japan, and Japanese held Manchuria, were not able to use the API navigation to the target being forced to rely on full moon’s and good weather which permitting dead reckoning, absent the API, and celestial fixes along the route. Radar bombing which was in its infancy, which helped to provide navigational direction once over land with early positive results demonstrating improvements in navigation and bombing accuracy. GPS navigation would be the solution decades after the war, providing accuracy to within three yards sufficient for all weather navigation.