Maj. Mike Sadler, a World War II navigator on the trackless Sahara of North Africa, who guided Britain’s first special forces across sand seas on daring behind-the-lines night raids that blew up enemy aircraft on the ground and troops in their billets, died on Thursday in Cambridge, England. He was 103.

The death, in a nursing home, was confirmed by John Allcock, the secretary of the Special Air Service Regimental Association, a welfare organization for veterans of the elite task force of the British Army that Mr. Sadler had belonged to, a prototype for hit-and-run warfare and for the U.S. Army’s Delta Force and the Navy’s SEALs.

Mr. Sadler was one of the first recruits and the last surviving member of the S.A.S. from the year of its founding, 1941. Like a navigator at sea, he used stars, sun and instruments to cross expanses of the Libyan Desert, a wasteland almost the size of India, whose shifting, windblown dunes can be as changing and featureless as an ocean.

Compared with the commandos he guided on truck and jeep convoys — volunteer daredevils who crept onto Nazi airfields; attached time bombs to Messerschmitt fighters, Stuka dive bombers, fuel dumps and pilot quarters; then sped away as explosions roared behind — Mr. Sadler was no hero in the usual sense. Comrades said he might not have fired a single shot at the enemy in North Africa.

But he got his men to the targets — and out again. Without him, they said, the commandos could not have crossed hundreds of miles of desert, found enemy bases on the Mediterranean Coast, destroyed more than 325 aircraft, blown up ammunition and supply dumps, killed hundreds of German and Italian soldiers and pilots, or found their way back to hidden bases.

“His navigating skills were legendary,” wrote Sean Rayment, the author of the book “Tales From the Special Forces Club: Mike Sadler’s Story” (2013). He said Mr. Sadler’s skills had “helped to ensure the success of some of the S.A.S.’s most spectacular missions during the North African campaign.”

Mr. Sadler, who grew up in England, was working on a farm in Southern Rhodesia, a British colony in southern Africa (now Zimbabwe), when the war began. He joined a Rhodesian regiment and in 1941 was posted to a British Army anti-tank unit in the desert near Egypt’s border with Libya, preparing to meet the German invasion of Gen. Erwin Rommel’s new Afrika Korps.

On leave in Cairo, Mr. Sadler met members of a new unit, the Long Range Desert Group, a small band of adventurers who conducted reconnaissance behind enemy lines and were training to ferry S.A.S. raiders on combat missions. Intrigued, Mr. Sadler won permission to join the desert group.

The S.A.S. had already tried a parachute attack behind the lines, but its planes were spotted, the element of surprise was lost, and the mission failed with heavy losses. The S.A.S. commander, Lt. Col. David Stirling, had another plan, however — to stage raids with trucks.

The North African war was being waged mostly along coastal areas, where Axis airfields and bases were strung out. Since Axis defenses were largely focused on Allied attacks from the sea, Colonel Stirling believed that a small, mobile force coming out of the desert at night could surprise the enemy — provided it could find its way.

Mr. Sadler was intrigued by desert navigation. “What amazed me,” he told Mr. Rayment, “was that even with the vast, featureless expanses of the desert, a good navigator could pinpoint his exact location by using a theodolite, an air almanac and air navigational tables, and having a good knowledge of the stars.”

He spent weeks studying navigation techniques, including use of a theodolite — a telescopic device, with two perpendicular axes, used mainly by surveyors, for measuring angles in the horizontal and vertical planes. It was not unlike the sextant used by mariners to fix positions at sea.

Ben Macintyre, the author of “Rogue Heroes: The History of the SAS, Britain’s Secret Special Forces Unit That Sabotaged the Nazis and Changed the Nature of War” (2016), wrote that Mr. Sadler’s remarkable skills in desert navigation were as much art as science, especially because his celestial observations had to be taken on uneven desert terrain.

“Desert navigation, like its equivalent at sea, is largely a matter of mathematics and observation, but the good navigator also relies on art, hunch and instinct,” Mr. Macintyre wrote. “The uneven ground caused the shadow on the sun compass to tilt this way or that, requiring the navigator to compensate. Sadler had uncanny, almost unerring ability to know where he was, where he was going, and when he would get there.”

(Mr. Macintyre’s book is the basis of a current BBC television series, “SAS: Rogue Heroes,” in which Mr. Sadler is played by Tom Glynn-Carney.)

To Mr. Sadler’s commandos — ragtag buccaneers in Arab headdresses and pirate beards — the Libyan Desert was an otherworldly mystery, stretching 1,000 miles south from the Mediterranean and 1,200 miles across, from the Nile to the mountains of Tunisia, a bone-dry realm of howling winds and dead silence, of dunes as tall as a 15-story building, rocky escarpments, hidden wadis and temperatures that could soar to 140 degrees by day and plunge below freezing at night.

Mr. Sadler’s first attack mission was a truck convoy in December 1941. “It was the S.A.S.’s first ground operation after the earlier failed mission, so a lot rested on it,” Mr. Sadler recalled. “My job was to navigate from the Jalo Oasis to the German airfield at Tamet.” It took two days and three nights to cross more than 400 miles of desert. The team reached its target without being detected.

In the dark, the commandos sneaked onto the airfield and attached bombs with timing devices to 30 aircraft. Afterward, they planted bombs at ammunition and fuel dumps and at a building housing 30 Italian pilots and an unspecified number of German pilots, then met Mr. Sadler at a rendezvous. The explosions began as the saboteurs sped away. Intelligence reports later said that 24 aircraft had been destroyed and that virtually all the German and Italian pilots had been killed in their quarters.

Mr. Sadler was recognized as one of the heroes. He was promoted to corporal, awarded the Military Medal and assigned to Colonel Stirling’s S.A.S. planning staff as the principal navigator for future missions, including attacks on airfields at Surt, El Agheila and Nofilia and supply dumps along Rommel’s lengthening advance eastward.

By July 1942, the S.A.S., with a force of 100 men, had acquired a consignment of four-wheel-drive American jeeps. Each jeep was stripped of nonessential parts, including the windshield, and fitted to carry extra fuel, water, ammunition and rations for longer missions. Each carried a pair of Vickers K machine guns. There was also a new attack plan.

Axis commanders were now aware of the danger of British raiders from the desert. The S.A.S., a victim of its own success, faced strengthened Axis guard mounts at its airfields, with a sentry at every plane. In response, Colonel Stirling proposed to give up sneak attacks for more direct force — a mass attack of jeeps with the power of Vickers guns, which fired 1,200 rounds a minute.

With Mr. Sadler navigating, in mid-July the commandos reached their target: the German airfield at Fuka, near Sidi Haneish, a desert base for Junker 52 transport planes and, not far from the Mediterranean coast, a major staging area for Rommel’s push into Egypt. At the edge of the airfield, the British fired a green signal flare into the sky and 18 S.A.S. jeeps roared down the tarmac and opened fire at parked planes on both sides.

“The vehicles drove in formation, as had been rehearsed the previous evening, and began to let rip into the parked aircraft,” said Mr. Sadler, who was posted at a corner of the field to pick up any wounded men. “The desert airfield seemed to be packed with every aircraft the Luftwaffe had deployed to North Africa — Stukas, Messerschmitts and the all-important JU52s.

“The Vickers were firing a mixture of ball and tracer ammunition at the maximum rate and soon the aircraft began to burst into flames. Although the German guards were not the primary target, they too were cut down by the enormous weight of fire. It wasn’t a battle as such, just a quick raid which really didn’t last more than about 10 minutes. Only one of our chaps was hit and killed on the field. Everyone else got away one way or another, and we destroyed 20 or 30 aircraft.”

A thick sea mist covered the jeeps’ retreat into the desert, where, as planned, they scattered. They later reassembled at a prearranged rendezvous and headed home. “The entire party eventually made it back to the base more or less intact,” Mr. Sadler recalled. “The tactic of the ‘mass jeep raid’ was regarded as a total success by Stirling and the S.A.S.”

But a September 1942 attack at Benghazi was a disaster for the S.A.S., which lost a quarter of its men and three-quarters of its vehicles. Mr. Sadler was promoted to lieutenant. In January 1943, he guided his last S.A.S. mission, crossing Libya to Tunisia, where his entire 15-man group was captured by a German patrol.

In one of the epic stories of the North Africa campaign, Mr. Sadler and two sergeants escaped from the Germans and, with only a goatskin carrying brackish water, crossed 110 miles of desert on foot in five days. Hostile Bedouins stoned them, bloodying their heads, and stole their warm clothing, leaving them to shiver through freezing nights.

Starving except for a few dates, they were exposed to windblown sands that scraped them like sandpaper, a relentless sun that burned and blistered their faces, and swarms of flies that enveloped and tormented them. On the hot sands, their feet were masses of blisters after a few days. When they finally reached Free French lines, they looked like half-dead castaways in rags.

“We had long hair and beards and were looking very bedraggled,” Mr. Sadler recalled. “Our feet were in tatters — I don’t think we looked very much like soldiers.”

French sentries brought them in. They were held at gunpoint at a hotel in Gafsa, an ancient Tunisian town that had been conquered by Romans, Vandals and Arabs and more recently by Italians, Germans, French and Americans. Suspicion had ruled Gasfa for millenniums: The men from the desert were turned over to the Americans, who thought they might be German spies.

The mix-up was straightened out with the help of a bottle of whiskey and a group of Western news correspondents who happened to be there, including A.J. Liebling, the celebrated American journalist for The New Yorker. He smelled a good story and interviewed the men. His article in the magazine of Nov. 17, 1943, introduced Americans to a new kind of warfare and the first accounts of S.A.S. exploits in North Africa.

At the end of a grueling day, Mr. Liebling related, “a G-2 (intelligence) officer came out of the staff tent” to talk to the Britons. “He had a bottle of whiskey with him, which was an excellent idea, because they were pretty well done in by that time. After half an hour, he climbed out and told us that he thought they were all right.”

Willis Michael Sadler — known to friends as Mike — was born in London on Feb. 22, 1919, to Adam and Wilma Sadler and was raised in Stroud, a village in Gloucestershire about 110 miles to the west. His father was the manager of a plastics factory. Mike attended the Oakley Hall School in Cirencester and the Bedales School in Hampshire. After graduation in 1937, he moved to Southern Rhodesia, his imagination fired by boyhood tales of adventure in a land of lions and elephants. With family connections, he got a job on a tobacco farm, where he worked until the war broke out.

After his North Africa adventures as a desert navigator, Mr. Sadler returned to England and in 1944 parachuted into France after the Allied invasion of Normandy. He participated in sabotage operations against German occupation forces and won the Military Cross for bravery in action behind enemy lines.

He and his wife, Patricia, whom he married after the war, had a daughter, Sally Sadler, who survives him. His wife is deceased. Until he moved to his Cambridge nursing home a couple of years ago, he lived in Cheltenham, Gloucestershire, 90 miles west of London.

After the war, he went on a one-year expedition to Antarctica with an S.A.S. colleague, Maj. Blair (Paddy) Mayne, who was Colonel Stirling’s successor in the S.A.S. Mr. Sadler later joined the British Foreign Office for what may have been classified work. Friends and journalists who interviewed him said he steadfastly declined to discuss his postwar activities beyond saying it was “foreign service work.”

Mr. Sadler had gradually lost his eyesight, but he marked his 100th birthday in 2020 with a celebratory gathering of friends at the Special Forces Club in London. “He spoke to me enthusiastically about it on the phone,” his friend Dominique Legrand said, “and his voice was as energetic as ever.”

Alex Traub contributed reporting.

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