The crucible of World War II displayed the glider’s potential—and revealed its limitations.
Although the glider was among the earliest forms of aircraft, its military possibilities were not explored until the 1930s and not put to real practical use until World War II. The glider is also unique so far among combat aircraft in that its operational use was limited solely to that conflict.
As a result of some spectacularly successful operations conducted by German glider troops during the war’s early stages, the assault glider concept came to be widely adopted by armed forces throughout the world. Those early German successes proved to be short-lived, however, and heavy losses during later operations led to confidence in gliders diminishing among Axis and Allies alike.
In a sense, the military glider can trace its origin to the Treaty of Versailles and its restrictions on the development of German aviation following World War I. The Germans discovered that they could circumvent many of those restrictions by developing and operating nonpowered aircraft. To a greater extent than in other countries, therefore, glider flying became a widespread sport in Germany between 1919 and 1939. By the same token, German aviation engineers became experts in designing highly efficient gliders.
The precursor to the military assault glider was a meteorological observation glider designed in 1932 by Alexander Lippisch and Walter Georgii. Known as the OBS, the glider could carry a pilot and two observers, as well as a considerable quantity of scientific instrumentation. Chancellor Adolf Hitler examined the OBS at Munich in 1934 and became intrigued with the possibility of developing a larger glider as a vehicle to deploy assault troops behind enemy lines. The result was the world’s first operational assault glider, the DFS 230.
Developed in 1937 by the Deutsches Forschungsinstitut für Segelflug (German Research Institute for Sailplanes), the DFS 230 could carry a pilot and nine troops. The glider had a wingspan of 72 feet, 1 inch and was 36 feet, 10 inches in length. Its high-wing monoplane configuration enhanced flying stability and kept the wings reasonably clear of ground obstructions while landing. Made of welded steel tubing and fabric, the DFS 230 was simple and inexpensive to build, and was intended to be expendable. It set a pattern that other military transport gliders were to emulate.
The DFS 230 was normally towed by a Junkers Ju-52/3m trimotor transport plane at a speed of 130 mph. Because the glider had no brakes, it took off from a jettisonable set of wheels and landed on a simple skid. A later version, employed during the rescue of Italian dictator Benito Mussolini from his mountaintop prison in the Gran Sasso by SS commandos and members of the 1st Fallschirmjäger Division under the command of SS Major Otto Skorzeny on September 12, 1943, used retro-rockets to reduce the landing run still further. More than 1,600 DFS 230s were built, including one experimental example with an auto-rotating rotor in place of conventional wings.
May 10, 1940, the day the Germans launched their offensive on the Western Front, also saw the first combat deployment of glider-borne troops. Their objective was Fort Eben Emael, which guarded two bridges over the Albert Canal that were of vital strategic importance to the German army’s plan to invade France through Belgium. A modern fortress containing numerous heavy guns and a 750-man garrison, Eben Emael was generally thought to be impregnable by military experts. A total of 29 DFS-230s were dispatched to secure the western side of the bridges and take the fortress. The Belgians managed to blow up one of the bridges, but after 30 hours of fighting, the small contingent of glider troops succeeded in capturing the other bridge intact—together with the fortress.
The spectacular success of the assault on Eben Emael spurred the world’s military leaders to consider the potential value of gliders to their own respective armies. Seemingly overnight, nearly every army in the world was forming airborne units and developing its own special gliders with which to transport them.
The Germans followed up their success by quickly developing a larger class of glider for more ambitious airborne operations. The type selected for production, the Gotha Go-242, was ordered off the drawing board in the autumn of 1940. In addition to its two pilots, the glider could carry 21 troops or up to 9,000 pounds of equipment. The Go-242’s novel pod and twin-boom configuration, in which the rear of the central fuselage nacelle opened up for access to the cargo hold, anticipated the design of the U.S. Air Force’s Fairchild C-119 transport by nearly a decade. By the time the Go-242 was phased out of production in 1944, 1,528 examples had been built for the Luftwaffe, including 133 fitted with engines as powered transports.
Germany’s most ambitious glider project, however, was the development of immense tank-carrying gliders for the invasion of Britain. That operation had been postponed, but ostensibly not canceled, after the Luftwaffe’s failure to defeat the Royal Air Force in the fall of 1940. The huge gliders were designed to carry an 88mm Flak (Flug Abwehr Kanone, or anti-aircraft) gun and its tractor, a self-propelled assault gun, a Mark IV medium tank, 200 troops or up to 44,090 pounds of cargo. Two firms, Junkers and Messerschmitt, were ordered to submit competing designs to fill the requirement within 14 days. The prototypes they produced were then and will probably remain the largest nonpowered aircraft ever built.
The Junkers Ju-322 was virtually a flying wing, with only a vestigial fuselage projecting astern and no nose at all. Its cargo was loaded through doors in the leading edge of the 203-foot wing, flanked by a pair of open machine gun pulpits reminiscent of a bomber of World War I vintage. Appropriately nicknamed the Mammut (mammoth), the Ju-322 was doomed to failure by the Luftwaffe’s insistence that it be built entirely of wood. The late Hugo Junkers had been one of the pioneers of all-metal aircraft design, and his firm had built nothing but airplanes with metal airframes since 1915. Consequently, the Junkers firm possessed neither the expertise, the materials nor the time to successfully construct the world’s largest wooden airframe. Only one Mammut was built before the project was canceled in favor of its more promising Messerschmitt competitor.
Unlike Junkers, Messerschmitt had been allowed to employ a mixed metal and wood structure for the airframe of its glider. Messerschmitt also took a comparatively conventional approach in the layout of its design, known as the Me-321 Gigant (giant). The Gigant was a high-wing monoplane with a span of 180 feet and a length of 92 feet. Access to the cargo hold was provided through a pair of enormous clamshell doors in the fuselage nose. The glider’s 44,090-pound payload was nearly twice its empty weight. The Luftwaffe acquired a total of 200 Gigants, and a few were used on the Eastern Front before being withdrawn in 1943.
The Gigant’s principal limitation stemmed from the Germans’ lack of an aircraft capable of towing it. One frightening solution involved the Troika-Schlepp, a trio of Messerschmitt Me-110 twin-engine fighters linked together in a V-formation. On one memorable occasion, an Me-321 with 200 troops aboard stalled shortly after takeoff, resulting in a catastrophic crash that killed everyone in all four aircraft. Another bizarre towing solution was the Heinkel He-111Z Zwilling (twin), a pair of Heinkel He-111H twin-engine bombers, joined together by a common wing center section incorporating a fifth engine.
In the end, the Luftwaffe opted for the most obvious solution to the problem by simply mounting six engines on the Gigant’s wings, thus transforming it into a powered transport. Messerschmitt built 198 examples of the Me-323, as the powered version was known, during 1941. The Me-323 performed well enough, but proved highly vulnerable to fighter attack. On one occasion a whole squadron was decimated by RAF fighters and bombers while attempting to airlift supplies across the Mediterranean Sea to the Afrika Korps.
One notable difference between German and Allied gliders was that the Germans gave some consideration to defensive armament. Many DFS 230s were armed with a flexible machine gun atop the fuselage and a second fixed forward-firing machine gun strapped to the side of the nose. The Go-242 could carry up to four machine guns, and the huge Gigants fairly bristled with them. In contrast, Allied gliders generally had no defensive firepower at all, with the exception of the weapons carried by the troops themselves.
By far the most improbable German glider was not a transport at all but a fighter. The Blohm und Voss Bv-40 appeared toward the end of the war, when the Luftwaffe was desperately seeking an antidote to the U.S. Eighth Air Force’s massive daylight bombing campaign. The idea was that a compact glider with a prone pilot would present too small a target for enemy gunners to hit. Armed with two 30mm cannons with 35 rounds of ammunition each, the little gliders were to be towed aloft by single-seat fighters and released above enemy bomber formations, at which point they were supposed to make a single firing pass and return to their base. The dubious project reached the stage where a prototype was actually test flown, but saner minds apparently prevailed, and the program was terminated before the glider-fighter entered production.
The German High Command’s enthusiasm for airborne assault operations, which had reached its peak after Eben Emael, began to wane after its Pyrrhic victory on Crete in May 1941. The assault on Crete was the first really large-scale airborne operation in history, and the Germans had every reason to be optimistic about the outcome. The Allied forces occupying the island—Greeks, British, Australians and New Zealanders—had recently been withdrawn from the Greek mainland after fighting a losing battle against an overwhelming German invasion force, leaving much of their equipment behind. To make matters worse, the RAF had only about a dozen fighter planes on the island, augmented by a few more from the Fleet Air Arm, while the Luftwaffe had more than 1,200 aircraft at its disposal, including 493 transports and 80 transport gliders. In the Allies’ favor, however, was the fact that most of Crete consisted of steep, mountainous terrain. There were relatively few places where airborne troops could safely land, and those areas had been heavily fortified. In consequence, many of the German airborne troops were killed by groundfire before they ever landed.
Ultimately, enough surviving airborne troops secured a foothold on Crete—including the crucial airfield at Maleme—for mountain troops of the 5th Gebirgsjäger Division to be airlifted in aboard transport aircraft. The deployment of those reinforcements compelled the Allies to evacuate Crete. It was the first time an island was successfully invaded entirely from the air, but in the process the victorious German airborne forces suffered a blow from which they never fully recovered. In 11 days they had sustained 30 percent casualties and lost 54 percent of their transport planes. Among the casualties were many valuable officers, including the commander of the 7thFallschirmjäger Division, who perished when his glider crashed. After Crete the Germans continued to use gliders for transporting supplies and for limited commando operations, but their high command never sanctioned another airborne assault of comparable scale.
If Crete dampened German confidence in the assault glider concept, it had the opposite effect on the Allies. From 1940 on, Britain increasingly regarded airborne assault as an important component in the proposed opening of a second front in Europe. In typical British fashion, their gliders were given alliterative names of antique warriors—beginning with the letter “H,” such as Hotspur, Hengist, Horsa and Hamilcar.
The General Aircraft Hotspur, the first and smallest of the British gliders, was roughly analogous in size to the German DFS 230. Designed to carry a pilot and seven troops, the Hotspur was quickly rendered obsolete by a change in policy that called for an emphasis on larger-capacity, cargo-carrying gliders. Although just over 1,000 Hotspurs were built, they were utilized only for training purposes. First flown in January 1942, the Slingsby Hengist could carry 15 troops, but only a few were built because of the availability of the similar sized but more versatile Waco CG-4A glider from the United States. Seven hundred forty of these were operated by the British under the name of Hadrian.
The Airspeed Horsa, which was the most numerous of the British gliders, appeared in September 1941. The Horsa could accommodate up to 25 troops or about 7,000 pounds of cargo, and had a hinged nose for easier access to the cargo hold. The glider could also be fitted with a drag chute to reduce the landing run. At one point, the British considered using the Horsa as a bomber, although it is unclear how that could have been practical. A total of 3,655 Horsas were built, and they were widely used by the Allied forces, including the U.S. Army.
Britain’s largest glider was the General Aircraft Hamilcar, which like the others was of wooden construction. The Hamilcar was intended as a specialized tank-carrying glider, but unlike the overambitious German Mammut and Gigant projects, it was designed to accommodate only light tanks. It could also carry a 17-pounder antitank gun or a field gun, along with their towing vehicle, or a payload of 17,500 pounds. With a length of 68 feet and a span of 110 feet, the Hamilcar was large but not as vast and unwieldy as its German counterparts. A total of 412 Hamilcars were built, and the heavy weapons they carried provided useful support for the airborne troops. That was particularly the case at Arnhem in September 1944, when British paratroopers unexpectedly found themselves facing an entire German panzer division.
The tanks that the Hamilcar was built to carry were either the British Tetrarch or American M-22 Locust. Both vehicles carried a crew of three and weighed about eight tons. The Tetrarch mounted a 2-pounder antitank gun and a .303-inch machine gun, while the Locust carried a 37mm gun and a .30-caliber machine gun. Both tanks had less than an inch of armor and were incapable of taking on German panzers on anything approaching equal terms. Nevertheless, they were useful for reconnaissance and for providing support against enemy strongpoints.
Gliders were not the only method considered for depositing armored vehicles behind enemy lines, however. The British, Soviets and Japanese all investigated the possibility of developing a set of disposable wings that would produce a flying tank. The so-called carrier wing scheme never got beyond the drawing board stage in Japan, and the British canceled it because of the Hamilcar’s success. Soviet designer Oleg Antonov, however, actually built a set of biplane wings and tail assembly, and fitted them to a 13,000-pound T-60 light tank. An attempt was made to fly the Krylyataya Tanka (winged tank) in December 1942, but even the most powerful Soviet aircraft available, the Petlyakov Pe-8 four-engine bomber, proved insufficient to get it off the ground. The legendary Ilyushin Il-2 Shturmovik ground-attack aircraft was destined to remain the only flying tank in the Soviet inventory.
The ubiquitous Jeep has been credited with the ability to do anything, and photographic evidence proves that when the British fitted it with an autorotating rotor and streamlined tail assembly in 1943, it could indeed fly. The Rotobuggy, as the device was called, had a maximum towing speed of 150 mph. It could also take off and land as slowly as 36 mph and, in fact, first flew while being towed by a Bentley automobile. The Jeep’s rugged suspension proved able to absorb landing loads of up to 11Gs. Although the design turned out to be feasible, the scheme was abandoned due to the availability of more practical alternatives in the form of the Horsa and Hamilcar gliders.
One distinct advantage British glider forces enjoyed over their German counterparts was an abundance of suitable towing aircraft. The Armstrong-Whitworth Whitley, an obsolete night bomber, got a new lease on life as a paratroop transport and glider tug. During the later stages of the war, when RAF Bomber Command replaced its Short Stirling and Handley-Page Halifax four-engine heavy bombers with Avro Lancasters, those aircraft were also made available as glider tugs.
Another important British glider tug was the Armstrong-Whitworth Albemarle, which resulted from a 1938 emergency program to provide an alternate source of bombers in case of a shortage of more sophisticated types like the Vickers Wellington. The Albemarle was specifically designed to be built out of nonstrategic materials by companies outside the aircraft industry, such as furniture factories. Under the circumstances, it was inevitable that the Albemarle should prove to be a mediocre combat aircraft. Since the expected shortfall of more suitable planes never materialized, the Albemarle was never used as a bomber, and the program was terminated in 1943. By then, 600 Albemarles had been completed, for which the RAF had to find a suitable role. Apart from a few that were transferred to the Soviet Union, the redundant bombers ended up providing a valuable service to the Allied cause as glider tugs.
By far the largest producer of gliders during WWII was the United States. Its principal type was the Waco CG-4, a simple-looking aircraft with high-set, strut-braced wings, 83 feet, 8 inches in span, and a fuselage 48 feet, 4 inches long. Of mixed wood and metal construction, it could carry two pilots and 15 troops. The only major change made to the original CG-4 design was the addition of a hinged nose in the “A” model, enabling it to carry a Jeep or a 75mm howitzer. The CG-4A could carry 3,800 pounds, 100 pounds more than its empty weight. First flown in 1942, a total of 12,393 CG-4As were produced by 16 manufacturers.
Although production centered on the Waco CG-4A, that type was not the only glider tested by the United States. Experimental types ranged from small amphibious gliders for the Navy to large tank-carrying Army gliders. One experimental program involved the conversion of a Douglas C-47 into a glider by removing the engines. Redesignated the XCG-17, the C-47 proved to be as efficient a flying machine without engines as it was with them. The U.S. Army Air Forces, however, apparently decided it had better uses for the versatile C-47 with its power plants than without them.
By far the most original U.S. glider design was the unique Cornelius XFG-1. First flown in 1944, the XFG-1 was intended as a flying fuel tank. It might have proved useful supplying Lt. Gen. George S. Patton’s Third Army, which had a habit of overreaching its supply lines. The glider was also visualized as a jettisonable auxiliary fuel tank, to be towed behind long-range bombers. The XFG-1’s cylindrical fuselage was 29 feet, 2 inches long and had a capacity of 677 gallons. It had forward-swept wings with a span of 53 feet, 8 inches and possessed no horizontal tail surfaces. Although a cockpit was provided under a fighter style canopy, the XFG-1 was designed to be automatically stable and thus operate without a pilot if necessary. Two XFG-1s were built, but the project was canceled when one of them crashed during a test flight in 1945.
If the United States was the principal Allied producer of gliders, it was also the principal source of glider tugs. When the U.S. Army Air Forces’ Troop Carrier Command was formed in 1942, its principal towing aircraft was the military version of the Douglas DC-3. Under a wide variety of designations, including C-47, C-53, R4D, Skytrain, Skytrooper, Dakota and Goony Bird, the ubiquitous DC-3 served in every Allied air force including the Soviet Union, which produced its own version called the Lisunov Li-2. Nearly 13,000 DC-3s were built, and General Dwight D. Eisenhower described it as one of the four principal instruments of Allied victory (along with the Jeep, the bazooka and the atomic bomb).
The availability of huge numbers of American Waco CG-4As, along with British Horsas and Hadrians, ensured that Allied airborne forces would play a major role in the liberation of Europe. They first went on the offensive during the invasion of Sicily on July 9, 1943, but the results were not encouraging. Although the troops acquitted themselves well, many of them were deployed in the wrong places or were not engaged at all. Approaching their objectives at night from the sea and under fire, many of the tug and glider pilots became disoriented and were unable to locate their designated landing zones. Some gliders crashed on landing, inflicting heavy casualties on their helpless occupants. More than half of them were released too far offshore and landed in the sea, drowning all aboard. Given the choice, many airborne troops considered dropping into enemy territory by parachute a safer proposition than gliding into battle.
It should be noted that the pilots assigned to fly gliders did not receive as high a level of training as those assigned to other flying services. British glider pilots, most of whom were sergeants, were members of the Army’s Glider Pilot Regiment rather than the RAF. They were regarded as soldiers rather than aviators and were required to fight alongside the other troops once their gliders were on the ground.
American glider pilots also belonged to the Army, but unlike most of their Army Air Forces colleagues, they were not commissioned officers, nor were they required to be college graduates. Even the wings they wore were different from those worn by regular Army pilots, although they were eventually granted the rank of flight officer, which carried warrant officer status. Unlike their British counterparts, American glider pilots were not required to fight on the ground.
Although Allied gliders continued to play an important part in the European campaign, most notably in the Normandy invasion on June 6, 1944, and during Operation Market-Garden in September, their limitations became increasingly manifest. In addition to losses from enemy fire or hard landings, many gliders failed to reach their landing zones due to broken towlines, faulty navigation, premature release or mechanical problems with their tow planes. Another shortcoming was the fact that gliders required a relatively large open space in which to land. That problem was underscored during the assault on Arnhem where due to topographical limitations the gliders were unable to land closer than five miles from their objective.
The Soviet Union was the only country other than Germany to have experimented with military gliders prior to WWII. The Red Army maintained the world’s largest paratroop force as early as the 1920s. The development of transport gliders began in the early 1930s, but it was restricted to experimentation until 1940, when Oleg Antonov’s relatively small A-7 was ordered into production. Roughly equivalent in size to the German DFS 230 and the British Hotspur, the A-7 could accommodate a pilot and nine troops. About 400 A-7s were built, and although they were widely utilized, their use by the Russians was on a modest scale in comparison with the Germans and the Western Allies. A-7s were often employed for landing sabotage teams behind enemy lines and for supplying weapons to partisan units. The Soviets also found gliders useful for supplying encircled army units. On one occasion in November 1942, gliders transported a supply of badly needed antifreeze to Soviet tank units engaged in the Stalingrad campaign.
In the Far East, Japan built and tested a number of glider designs. One, the Kokusai Ku.8-II, was based on the design of a prewar powered light transport airplane and achieved a modest level of production. A few Ku.8-IIs were encountered by American forces during the reoccupation of the Philippines in 1944. On the whole, however, Japanese interest in gliders was not as great as in the West, and they played little part in the Japanese war effort.
Other belligerent countries that experimented with gliders included Italy, Hungary, Australia and India. Assault gliders were also tested in neutral countries such as Sweden, Turkey and Argentina. None of them entered production, however.
The military glider did not disappear immediately after the end of World War II. New prototypes were produced in reemerging nations such as Czechoslovakia, Yugoslavia, Nationalist China and France.
In the United States, the postwar trend was toward more sophisticated all-metal nonexpendable gliders that resembled engineless transport planes. Typical of that trend were a series of designs by Chase Aircraft that were intended from the outset to operate both as gliders and as powered transports. A propeller-driven version of the last such glider, the XCG-20, went into production in 1953 as the Fairchild C-123 light tactical transport.
When the glider program was terminated in 1950, the second XG-20 glider prototype was fitted with four General Electric J47-GE- 11 engines. Redesignated the XC-123A, it became the world’s first jet-propelled military transport aircraft, but the restrictions posed by takeoff and landing areas kept it from going into production.
The last assault glider design to attain production status—the Soviet Yakovlev Yak-14 in 1948—was a high-wing monoplane of wooden construction, capable of carrying 35 troops or an 8,000-pound payload, and equipped with a hinged nose section to provide access for vehicles or cargo. A total of 413 Yak-14s were built and used by the Soviet and Warsaw Pact armies until they were retired in 1954.
Despite the initial success of German glider forces, the operational shortcomings of the military glider became more obvious as WWII progressed. In the immediate postwar period, a new aviation technology, the helicopter, offered a more attractive alternative. Although it lacked the absolute silence of the glider, the helicopter had the ability to transport its occupants or cargo to the exact spot where they were needed. For that matter, since a helicopter could hover over its objective, it did not even need to land to fulfill its mission.
Gliders saw no use during the Korean War. By the time of the Vietnam War, the U.S. Army’s gliderborne troops of World War II had been completely replaced by a formidable new helicopter-borne force, known as the Air Cavalry.
A frequent contributor to Aviation History, Robert Guttman recommends the following for additional reading: History of the World’s Glider Forces, by Alan Wood; and The World’s Worst Aircraft, by James Gilbert
Originally published in the July 2006 issue of Aviation History. To subscribe, click here.
