[1.0] The Aerial Torpedo

v4.0.0 / chapter 1 of 8 / 01 jul 13 / greg goebel / public domain

* Most people would think that cruise missiles are a modern technology. However, the concept of an "aerial torpedo", a pilotless aircraft with a warhead that flies to a distant target and dives into it, has been around since the first World War. This chapter describes early experiments in aerial torpedoes.

Kettering Bug at USAF Museum



* In 1915, American inventor Thomas Edison and US Navy Secretary Josephus Daniels proposed that a board of prominent inventors be created to help the US prepare for possible involvement in the Great War in Europe. The "Naval Consulting Board" was put together, but did very little of practical use. One exception was the development of the first aerial torpedoes by Elmer Sperry and Charles Kettering.

Elmer Sperry was a bonafide genius with 350 patents to his name. While he worked in a wide range of fields, his main interest was feedback control, and he was one of its founding fathers. He had become well known to the military by developing feedback stabilization systems for warships to allow them to shoot accurately in rough seas. Just a few months before the beginning of the war, in June 1914, Lawrence Sperry, Elmer Sperry's daredevil engineer son, demonstrated a automatic gyrostabilizer that allowed a Curtis flying boat to fly straight and level without human intervention. After the war began, Elmer Sperry worked with the British Royal Air Force (RAF) to link the gyrostabilizer control system to a bombsight to keep a plane on course, while a bombardier lined up the target in his sights.

In 1916, the Sperrys incorporated a steering gyro along with the stabilizer gyro, resulting in one of the world's first "automatic pilot" systems, which they demonstrated that year. It was no big conceptual step from having an autopilot that could assist a human pilot, to having an airplane that didn't need a human pilot at all. In fact, such a weapon had been imagined as far back as 1891 by Sir Hiram Maxim, an American-born Briton who had invented the modern machine gun and had performed various inconclusive experiments with flying machines.

In 1916, Lawrence Sperry filed a patent for an aerial torpedo, featuring the following elements:

A wind-driven electrical generator was to provide power for the gyro motors and the servomotors that moved the aerial torpedo's flight control surfaces.

Elmer Sperry was enthusiastic about the aerial torpedo, believing that it would be such a destructive weapon that it would discourage people from starting wars. Such an attitude was common among arms developers before the horrors of the First World War suggested otherwise. In April 1917, the Naval Consulting Board approved Sperry's aerial torpedo project, and the Navy awarded the Sperry Gyroscope Company a $200,000 USD contract to build such a weapon. Sperry was to first install an autopilot system on conventional Curtis aircraft, and then work with Curtis to build a true aerial torpedo.

Tests of a Curtis N-9 biplane fitted with a autopilot went well, though the aircraft still carried a pilot to handle take-offs and to observe the flight. In November 1917, Curtis delivered the first purpose-built aerial torpedo airframe, which was powered by a two-cylinder engine. Sperry engineers installed the autopilot, while Lawrence Sperry test-piloted a modified aerial torpedo to help work out the bugs. He crashed about four times.

On 6 March 1918, the first known flight of a guided missile took place. The aerial torpedo climbed automatically from its launch and made a smooth, stable flight until the distance control automatically ended the test at a preset range of a thousand yards. Further tests of the purpose-built aerial torpedo did not go well, and Sperry engineers went back to the N-9.

* In the meantime, the US Army was working on their own aerial torpedo, with the project directed by Charles F. Kettering. Kettering had invented the automobile self-starter, and would become the first head of the General Motors Research Laboratory. Today his name is associated with the Sloan-Kettering Cancer Research Institute in New York.

After observing tests of the Sperry autopiloted aircraft in late 1917, Kettering was enthusiastic enough to agree to develop an aerial torpedo. Kettering felt the Sperry system was too complicated and wanted to build something cheaper and simpler. Orville Wright contributed his expertise to the development of the airframe for the Kettering aerial torpedo. Another engineering team designed the powerplant, a 30 kW (40 HP) air-cooled V4, which ultimately was to cost only $40 USD. A third team designed a cheap, portable launch system, consisting of a four-wheeled cradle riding on rails. Unfortunately, Kettering was unable to build a workable autopilot and had to call on Elmer Sperry for help. Sperry graciously lent his assistance.

The resulting Kettering weapon actually looked like a torpedo, fitted with dihedral biplane wings. The first tests began in September 1918, with the first full scale flight on 2 October, when it was given the name "Bug". The test was not a success, however. The Bug began flying in higher and higher circles until it ran out of fuel and fell to earth.

   _____________________   _________________   _______________________
   spec                    metric              english
   _____________________   _________________   _______________________

   wingspan                4.6 meters          15 feet
   length                  3.8 meters          12 feet 6 inches
   total weight            240 kilograms       530 pounds
   warhead weight          80 kilograms        180 pounds
   speed                   195 KPH             120 MPH / 105 KT
   range                   120 KM              75 MI / 65 NMI
   _____________________   _________________   _______________________

Other tests went better, and so the Army ordered a hundred prototypes. Then, in November 1918, the Armistice went into effect, and the government decided to combine the Army and Navy programs. Competitive tests favored the Sperry-Curtis weapon, and the Kettering Bug was abandoned. Further American work on aerial torpedoes fizzled out over the next few years.



* The British pursued aerial torpedoes in parallel with the American effort. In late 1915, Professor A.M. Low was asked to help develop a radio-controlled aircraft to intercept Zeppelin raiders and attack ground targets. The robot aircraft was designated "AT", which was supposed to stand for "Aerial Target" as a cover to hide the true nature of the weapon.

Low built the radio control system, which, unsurprisingly considering the technology at his disposal, was crude and heavy. In the meantime, aeronautical engineers built a small monoplane airframe for the AT, powered by a 37 kW (50 HP) Gnome rotary engine. Rotary engines looked like radial piston engines, but in a rotary engine the propeller was fixed to the engine block and the engine block spun on a shaft. They leaked oil at a great rate, started small fires on the ground under an aircraft when they were cranked up, and also, as it turned out, produced a lot of electrical noise. The first AT was flown in October 1916, but the noisy engine interfered with the radio control system. The AT was obviously unworkable and was abandoned, but other aircraft manufacturers were interested in the concept and took a shot at it.

The Royal Aircraft Factory at Farnborough built a monoplane with a wingspan of 6.7 meters (22 feet) and a two-cylinder air-cooled engine providing 26 kW (35 HP). The engine was designed by a company named "ABC", and was intended to operate for a minimum of two hours, making it one of the first purpose-designed expendable engines ever built. One of these aerial torpedoes was demonstrated in March 1917, only to embarrassingly crash immediately after launch. The Sopwith company attempted to build a biplane aerial torpedo with an ABC engine, but this aircraft was never completed. The exact number of different types of aerial torpedoes developed by the British during World War I and their details is unclear. What is clear is that little came of the effort.

* Work on automated aircraft continued in Britain after the war. In 1920, a standard Bristol F.2B fighter was fitted with radio control and flown successfully, though the aircraft still carried a human pilot as a backup. A radio-guided purpose-built aerial target was also tested in 1921. These efforts led to the interesting "Long-Range Gun With Lynx Engine (LARYNX)" aerial torpedo of 1927. This was a neat little monoplane with a radial engine and a gyroscopic control system, built by the Royal Aeronautical Establishment for the Royal Navy -- one suspects the "Long-Range Gun" label was a way of selling a newfangled idea to conservative admirals. One LARYNX was successfully launched from a destroyer off the coast of England. A number of the missiles were flight-tested in the deserts of Iraq armed with a 113 kilogram (250 pound) warhead. Results of the tests were inconclusive.


Like the US effort, the British effort to build aerial torpedoes fizzled out. They did have success in converting de Havilland Tiger Moth trainer biplanes to training targets, known as "Queen Bees", with the Queen Bees either trailing target sleeves or operating in more assertive training roles.



* American and British work on aerial torpedoes revived somewhat in World War II. In 1940, Miles Aircraft of the UK proposed an aerial torpedo they called the "Hoop-la", and constructed a mockup. The Hoop-la was a neat little high-wing aircraft built around a 450 kilogram (1,000 pound) bomb, featuring a Gipsy Major air-cooled four-cylinder inline engine, a wingspan of 4.3 meters (14 feet), and an estimated speed of over 480 KPH (300 MPH).

While the accuracy of the Hoop-la would have undoubtedly have been poor, Miles Aircraft felt that it could hit a city. Swarms of Hoop-las coming in at low altitude at night would have given German air defenses a very hard time. The British Ministry of Aircraft Production was not interested in the Hoop-la, apparently because there was still some squeamishness about general attacks on cities. If there was such squeamishness, it didn't last long, since general military bombing of cities at night became RAF Bomber Command policy in a short time, but the Hoop-la remained dead.

* The Germans developed a series of aerial torpedoes, derived from studies performed in the 1930s by the Soviet Union into "composite" aircraft, in which big lumbering Red bombers carried fighters perched on top or dangling from the wings.

In 1941, the German Air Ministry (ReichluftMinisterium or RLM) began to investigate composite aircraft, and a suggestion was made that the scheme could be used to allow a fighter to guide an unmanned war-weary Junkers Ju-88 bomber packed with explosives to a target. The idea wasn't popular, but then experiments using a piggyback aircraft to tow a glider demonstrated the feasibility of composite aircraft, and interest in the possibility of using a piggyback fighter to direct a flying bomb aircraft increased.

The RLM authorized a development project codenamed BEETHOVEN to build such a weapon, and the result was the "Mistel (Mistletoe)" composite flying bomb, with the name derived from the fact that Mistletoe is a parasitic plant. The first Mistel flew in July 1943, and featured a Messerschmitt Bf-109E fighter fitted on a set of struts to the top of an unmanned, explosive-packed Ju-88A bomber. The piggyback fighter was wired to the bomber's throttles and flight controls. The fighter pilot took the composite into the air, flew to the target area, flew straight at the target, and then released his fighter from the bomber. The bomber flew into the target on autopilot. Although some sources mention that a few of the bombers were radio-controlled, it doesn't seem to have been general practice if it was done at all.

Improved Mistel versions were devised, using a Focke-Wulf Fw-190A fighter on top of a Ju-88G or Ju-88A. The operational version featured a Ju-88A-4 with the conventional nose and crew cabin removed, and a huge 3.5 tonne (7,720 pound) hollow-charge warhead with a long nose probe. Tests demonstrated that the Mistel's warhead could penetrate almost any thickness of reinforced concrete, and also made short work of a old French battleship used as a target.

Mistel 3C composite

The Luftwaffe high command became very enthusiastic about the Mistel. The Mistel went into operation in June 1944, and a few were used against Allied ships at the end of the month. Surprisingly, none of the Mistel hits actually sank a ship. A plan was cooked up for using Mistels in a heavy coordinated blow codenamed Operation EISENHAMMER (IRON HAMMER).

There were a confusing number of minor variants of the Mistel, with such features as reinforced landing gear for the Ju-88 to deal with the higher take-off weight, and Fw-190As with overwing tanks to provide greater range. A few Mistels were actually built with piloted Ju-88s for long-range "pathfinder" missions, where the Fw-190A was simply taken along to provide a fighter escort. Though over 250 Mistels were built, including some based on new-production Ju-88s, Operation EISENHAMMER never took place. The Mistels were expended in piecemeal attacks, mostly against bridges in hopes of stemming the flood of Allied forces towards Germany. Under unceasing pressure, the Luftwaffe was never able to accumulate enough Mistels to make the big blow.

Of course, the Germans also developed a jet-powered aerial torpedo that actually saw widespread use, the "Fi-103" or "V-1" flying bomb. This weapon is the subject of the next chapter.

* The Germans considered various other Mistel configurations, such as jet version, based on the Messerschmitt Me-262 jet fighter. This involved a piloted Me-262 with a glass nose to accommodate a bombardier lying on his stomach, propped on top of a pilotless Me-262 with a warhead nose. The entire contraption was to take off on a trolley that was discarded after take-off.

The Blohm und Voss company also proposed another Mistel configuration, in which a Dornier Do-217 bomber carried an 8 meter (26 foot) long, bulletlike, ramjet-powered missile perched on its back, while the missile carried a tiny piloted ramjet aircraft on its back in turn. The Do-217 would release the missile in a dive to allow operation of its ramjet engine. The pilot of the piggyback aircraft would fly the missile to its target, aim it at the impact point, ignite the aircraft's ramjet, and then release the missile and return home.

Blohm und Voss ramjet mistel

Illustrations of these concepts come across as a little preposterous, even by the standards of Mistel, and it seems they were never more than paper projects.



* America also investigated aerial torpedoes in World War II. The US Navy and US Army Air Forces (USAAF) worked on various aerial torpedo systems.

A senior US Navy admiral witnessed the British Queen Bee in operation in 1936 and found the concept very interesting, with a US Navy program then set up under Lieutenant Commander Delmar S. Farnhey. By 1937, Farnhey's team had converted a number of light aircraft to radio-controlled targets and used them in exercises. It is said that Farnhey invented the term "drones" for robot aircraft as a nod to the British Queen Bee.

The next year, 1938, Farnhey decided to try a bomb-carrying "assault drone" in naval exercises. It was shot down but the idea didn't go away, with Farnhey considering use of the newfangled television camera in such applications. In fact, RCA's Dr. Vladimir Zworykin, one of the prime movers behind the invention of television, had been promoting the idea of a television-guided assault drone for some time, but nobody in the military was listening until Farnhey got in touch with him. The first television-guided drone, using an RCA-developed television system, was demonstrated in 1940.

There matters more or less stood until the Japanese attack on Pearl Harbor on 7 December 1941. The US military was thrown into the war more abruptly than anyone had planned, and one of the results was consideration of a wide range of new weapons that might help win the war. A secret program to build an assault drone, codenamed Project OPTION, was formally begun in February 1942, under the direction of Commodore Oscar Smith, with assistance from Farnhey and Zworykin.

By April 1942, the project had performed a successful torpedo attack using an assault drone. Films of the exercise provoked high interest among the senior brass and civilian leadership, with OPTION raised in priority and plans to build 5,000 assault drones for deployment with 18 drone squadrons. One of the consequences of this good fortune for the drone program, however, was that critics began to hammer on the effort as a waste of resources.

Farnhey countered by directing the development of a low-cost assault drone, the "TDN-1", which was constructed by the US Naval Aircraft Factory and was built mostly of wood. The "TD" stood for "Torpedo Drone", of course, while the "N" was a code for the Naval Aircraft Factory. The TDN-1 featured a high wing, twin small piston engines, and fixed tricycle landing gear. It could carry a torpedo or 900 kilogram (2,000 pound) bomb nested under its fuselage, at a cruising speed of 280 KPH (175 MPH). A conventional cockpit could be swapped out for the TV control system for tests or ferrying. Only about 114 TDN-1s were built. The design was not well-suited for mass production and the TDN-1s ended up being used for evaluation and as targets.

Official enthusiasm for the assault drone concept began to fade, but Smith and Farnhey were moving ahead on a production assault drone, the "TDR-1", built by Interstate Aircraft Company of Los Angeles -- the "R" code in the drone designation was for Interstate Aircraft. The TDR-1's general configuration was much like that of the TDN-1 but it was much more practical to build, with a frame of steel tubing covered by molded wood. The frame was provided by the Schwinn bicycle company and the subcontractors for the woodwork included manufacturers of musical instruments. The two machines were externally similar, but easily told apart because the TDN-1 had a high-mounted wing and the TDR-1 had a low-mounted wing.

Interstate TDR-1 drone

The TDR-1 was powered by twin Lycoming flat-six air-cooled piston engines. Like the TDN-1, it could be piloted, and it was said to be very pleasant to fly, though not all that fast. The fixed landing gear could be ejected when the aircraft was on an attack run. However, the program was still on increasingly uncertain political ground, and it took intense lobbying by Smith and Farnhey to obtain approval for deployment of their "Special Task Air Group 1 (STAG-1)", which departed for the South Pacific in mid-May 1944.

The TDR-1s were controlled by Grumman Avenger torpedo bombers, modified to carry control systems and designated "TBM-1C". The radio control and TV reception antennas were carried in a retractable antenna dome in the Avenger's rear belly. The control system in the aircraft included a joystick and a remote control for the TDR-1's autopilot system. The autopilot remote control used, of a things, a telephone dial, with the appropriate autopilot control code set by just dialing a single digit -- one to drop a torpedo, one to arm a bomb, and so on. However, the control system only had four channels and so it was only possible to fly four TDR-1s at a time in the same attack.

The first attack was conducted on 30 July, on a derelict Japanese freighter, the YAMAZAKI MARU, that had grounded itself near Cape Esperance on Guadalcanal Island in the Solomons. Six TDR-1s, with four intended for the attack and two as backups, were committed to the mission, all armed with 900 kilogram (2,000 pound) bombs. Two cracked up on takeoff, two performed attacks that were frustrated by dud bombs, but two went off with very impressive bangs. It made for great film footage, but by that time the effort's standing was so low that Smith had to lobby very hard just to keep the program from being immediately canceled.

Beginning on 27 September 1944, STAG-1 conducted a series of attacks on Japanese installations on the island of Bougainville. When the attacks ended on 26 October 1944, STAG-1 had expended 46 TDR-1s in combat, with 37 performing attacks and at least 21 hitting their target. The Japanese found the attacks startling, believing that the Americans had taken up suicide attacks.

The end score seemed encouraging, but it wasn't enough to stave off cancellation. The TBM-1Cs were dumped into the ocean to dispose of them and the personnel reassigned to other duties. It was a bitter pill to swallow for the program's officers and men, but by that time the war was clearly going to be won by other weapons and the TDR-1 was no longer seen as particularly relevant. Apparently some further work was done a "TDR-3" that featured radial engines, but though a picture of such a machine survives, it may have been a mockup, and it's unclear if it ever actually flew.

It is also unclear in hindsight if killing off the TDR-1 was the wrong decision. The TDR-1 had some potential, but the television system was very crude, with poor contrast and resolution. It was only adequate for picking out large distinct targets in relatively bright daylight conditions, and the complexity of the bulky electronics suggested that keeping things working in rough field conditions would be troublesome. The video link back from a drone was also easily jammed; the Allies had quickly developed jammers to neutralize German radio-guided glide bombs, and there was nothing to prevent the Axis powers from developing simple jammers of their own to neutralize the assault drones.

Some TDR-1s were used as private sports planes for a few years after the war. Only one of the 200-some TDR-1s survives, as a static display at the US Navy Air Museum in Pensacola, Florida.

Interstate TDR-1 attack drone

* In early 1941, the USAAF, following up the work done on the Kettering Bug two decades before, awarded a contract to Kettering and General Motors to develop a new flying bomb, the General Motors "A-1". The A-1 was a radio-controlled monoplane that could carry a 225 kilogram (500 pound) bomb over a distance of 640 kilometers (400 miles) at a speed of 320 KPH (200 MPH). Like the original Kettering Bug, the A-1 was launched off rails on a trolley. A number of A-1s were built, but the program was disorganized and was canceled in 1943.

The USAAF pursued a series of other aerial torpedoes, under the general designation of "Controllable Bomb, Ground Launched", cryptically abbreviated as "BQ". The BQ series covered an interesting range of configurations, including purpose-designed weapons and conversions of the Fairchild AT-21 twin-engine crew trainer, as well as a single TDR-1 loaned from the Navy and evaluated as the "XBQ-4". However, the most ambitious and best known of the BQ weapons were radio-controlled conversions of "war weary" Boeing B-17 Fortress and Consolidated B-24 bombers, filled with explosives.

The converted Fortresses were given the designation of "BQ-7", and they were filled with 9 tonnes (20,000 pounds) of Torpex explosive. The BQ-7s were to take off under the control of a human pilot and copilot, who would bail out once the weapon was airborne, under remote control, and armed to explode. The roof of the cockpit was cut off to allow the crew to escape more easily. About 25 BQ-7s were produced under the codename APHRODITE. Crews referred to the bombers as "Weary Willies" or just "Willies", though this sounds like it was a general nickname for any war-weary aircraft. The BQ-7s were to be used in attacks on "hardened" German military installations under a plan known as Project PERILOUS. They were supposed to be accompanied to the target by a Lockheed Ventura director aircraft, along with piloted B-17 to provide navigation, as well as a Lockheed P-38 fighter to shoot down the flying bomb if radio control was lost.

There were a number of attempts to use the BQ-7 in combat, but the results were poor. One is said to have lost radio lock and circled an English city for some time, terrifying its controllers, and another is known to have crashed on British soil with a tremendous explosion, leaving a huge crater. The USAAF decided that PERILOUS lived up to its name only too well and abandoned the effort.

* The converted B-24s were given the designation "BQ-8", and were built as a joint US Navy / USAAF project. They were filled with 11,340 kilograms (25,000 pounds) of Torpex. They had radio control and a television camera mounted in the nose. Two BQ-8s, converted from the US Navy version of the B-24 known as the P4Y, were produced as part of Project ANVIL, which also involved attacks on hardened German military installations. They were accompanied by a Ventura control aircraft working in conjunction with B-17, which was fitted with the television receiving equipment.

The first ANVIL mission, on 12 August 1944, ended in disaster, exploding in mid-air with a tremendous blast. The two crewmen, Navy Lieutenants Wilford J. Willy and Joseph P. Kennedy JR, were obliterated. Joseph P. Kennedy JR was the eldest son of the prominent Joseph Kennedy family. Joe Kennedy JR was being groomed for the American presidency; younger brother John Fitzgerald Kennedy ended up taking his place in the White House. The second BQ-8 mission, on 3 September 1944, inflicted some damage on German facilities in Heligoland, but missed its intended target due to poor TV reception. The BQ series was abandoned. The poor showing of the BQ weapons was apparently a contributing factor to the cancellation of the TDR-1.

* Work on unpiloted aircraft continued after the war, with B-17s and other aircraft converted into radio-controlled drones, though in general they were used as targets and not as aerial torpedoes. In late August 1952, six Grumman F6F Hellcat fighters, which had been were converted to aerial torpedoes using improved technology based on that of the TDR-1 program, were used in attacks on a North Korean bridge, power plant, and railroad tunnel. They were controlled by Douglas AD-2Q Skyraider attack aircraft, and the hit rate was 50%.

As with the TDR-1, the results were encouraging, but the brass wasn't interested. Part of the reason was that by that time interest had moved on to jet-powered aerial torpedoes, or what would become known as "cruise missiles".