Navigation can be defined as the art and science of directing a vehicle from one place to another, knowing its position en route. For ships, trucks, and railway trains this can be considered in only two dimensions but for aircraft (or submarines) the third dimension--altitude--is vital. One of the most graphic examples of this is shown in the crash of the British dirigible R101.

The word "dirigible" simply means "steerable", and was first used in the phrase "dirigible balloon". About the turn of the century the German Count Zeppelin built and put into commercial service a number of the big gas filled cigars, and when the First World War began both the German army and the German navy were using airships. They performed considerable service, scouting for the High Seas Fleet at the Battle of Jutland, carrying ammunition, food and medicine to German troops cut off in German Southwest Africa, and bombing Britain. Before the war was over Britain and France had copied the German design, and dirigibles were extensively used to convoy merchant ships. No convoy, while under the escort of the non-rigid dirigibles which had been given the name "Blimp", ever lost a ship.

After the war, Britain set out to build a fleet of commercial dirigibles, very much along the German pattern. These airships possessed a rigid frame, as opposed to the non-rigid gasbag which is inflated to shape by the pressure of the gas inside, which is the design of the only airships now surviving, the familiar Goodyear airships.

After the end of the war, Britain decided to enter the airship business. In 1924 construction was begun on two large rigid dirigibles, R100 and R101. R100 was built by Vickers at Howden, while R101 was built at Cardington under government auspices. The designer of R100 was Barnes Wallis, who later was to design the huge bombs that No. 617 Squadron RAF, the famous "Dam-Busters", were to use to destroy the Mohn and Eder dams, and also the 22,000 "Grand Slam" bombs that sank the huge German Battleship "Tirpitz". R101 was designed by Lt. Col. V.R. Richmond. The two men apparently disliked each other, since they never visited each other during the five years the two big gasbags were in production.

When R100 got into the air, it proved itself able to make 81 mph, and produce a lift of 57 tons. R101, which first flew 14 October 1929, however could lift no more than 35 tons, and as a result had to be cut in two and lengthened to 777 feet, from its original 709 feet. Its diameter, 130 feet remained the same. While this was happening R100 flew to Canada in 571/2 hours, creating a sensation. When R101 took to the skies again on 2 June 1930, a ninety-foot tear developed in the skin, and the coxswain, "Mush" Oughton, had to fight to keep it steady despite severe control difficulties. Subjected to a chorus of criticism, the designers of R101 felt they had to demonstrate the worth of their big craft or lose their jobs. It was decided to fly to India, leaving England 4 October 1930, reaching Karachi on the 9th, and leaving India on the 13th to return to England by the 18th. Lord Thomson, the Secretary of State for Air, demonstrated his confidence in the big craft, built by government enterprise, by taking passage in R101. The airship had a Certificate of Aeronautics, which was given to the crew as the passengers filed aboard, but Thomson was unworried. "R101 is as safe as a house", he said, "except for the millionth chance."

On board as the craft left at 6:36 PM, 4 October 1930 were Lord Thomson's valet, James Buck; Wing Commander Colmore, the Directorate of Airship Development; six officials of the Royal Airship Works, which had built the craft, headed by Colonel Richmond; and 42 crew.

Four tons of water ballast were dumped on take-off, partly to assist one of the six diesel engines, which was balking. The weather forecast predicted 40 to 50 knot winds over France, with heavy clouds. R101 set off south.

In mid-Channel a foreman engineer of the Royal Aircraft Works looked out of a hatch to see whitecaps just below him. Checking on the altitude, he found it to be 700 feet. When he reported this, Lt. Cdr. N.G. Atherton, the officer of the watch, took the controls and climbed to 1000 feet. "Don't let her get below 1000 feet," he told the coxswain when he relinquished the wheel. Meanwhile, the ship's radio operator had sent a message to Cardington; "After an excellent supper, our distinguished guests smoked a final cigar and have now gone to rest."

The airship crossed the French coast and passed Poix Aerodrome, halfway between Abbeville and Gervais, a little northwest of Paris. Louis Maillet, in charge of the airport, wondered why the craft was so low, estimating its height at 300 feet. The navigator asked for a radio fix from Le Bourget, at Paris, confirming his position as half a mile from Poix.

A little later the secretary of the police station at Beauvais saw R101, still heading south. Louis Lechat, a jeweler, who saw the big airship at 1:00 AM, reported it as rolling and dipping. It was low enough to wake up the people of the town.

Just past Beauvais the craft nosed down. The coxswain could not pull it out of its dive. The first officer ordered the crew roused. "Prepare for a crash!" he shouted. R101 half-leveled, and then pitched into a second dive. It hit the ground, ploughed forward for a few feet, ripping off propellers, and then exploded. Two men managed to jump clear. All but one of the passengers were trapped in their beds, however, and when the death-roll was completed it contained 48 names.

The accident finished the airship in Britain. Even the successful craft, R100 was retired from service shortly afterward. No further lighter-than-air craft, except a few balloons, have since been built in Britain.

The crash possesses elements of mystery. Why did the crew stay so low? 700 feet could have been safe enough over the Channel, but when the aircraft flew over France it was soon over land which rose to 400 feet, leaving a scant 600 feet clearance, even if the altimeter contained no error. With high winds, there must have been a severe pressure gradient, which undoubtedly caused the altimeter to over read progressively more as it flew southwards. Furthermore, only a hundred miles or so ahead of it lay the Central Massif of France, with peaks up to more than four thousand feet. Perhaps the navigator wanted to stay low so that he would observe ground features to fix his position, but if this was the case, why did he ask for a radio fix from Le Bourget?

In any case, if the craft has been a few thousand feet higher there would most likely have been enough height to recover from its difficulties. To fly at such an absurdly low altitude, over rising ground, in bad weather, with an airship which had a history of control problems, was bad policy from any standpoint.

It is possible that the navigator, with marine techniques firmly in his mind, concentrated exclusively on his position in latitude and longitude, and forgot about the third dimension. Why the rest of the crew, however, never considered that the low altitude was dangerous, or at least imprudent, is also difficult to fathom. It is possible that the man at the controls, a coxswain, felt that the officers would look after such matters; his job was to keep the craft at the 1000 feet on the altimeter as ordered.

In any case, the aircraft crashed and Britain's hopes of lighter-than-air supremacy went up in flames along with its hydrogen. British aeronauts never had the chance to put into practice a lesson they learned from R101-that navigation also includes the third dimension.