In the years before World War Two, the US found itself in a unique--and difficult--situation. On one side of the country was the Atlantic Ocean. On the other side of the country was the Pacific Ocean. In those days before radar or satellites, the US could only know what was happening out in the open seas by going there and searching. Reconnaissance flights by aircraft, however, could only cover a relatively short distance near the coasts. The US needed another way to monitor the vast empty oceans, searching for approaching enemy fleets from Europe or Asia. And the method the Navy adopted was one of the oddest aerial projects ever attempted--the flying aircraft carrier.
The aerial vehicle that was best-suited for long-range reconnaissance over the oceans was the dirigible. Developed during the First World War, dirigibles were huge fabric balloons, supported by internal aluminum frames, and steered by external engines with propellers. Early dirigibles used internal gas bags filled with hydrogen for lift; later designs used safer helium instead. During World War One, German dirigibles, known as zeppelins, were used to make bombing runs from Germany to London. Later in the war, dirigibles were used as escorts for cross-Atlantic cargo convoys, to search for enemy submarines.
In 1929, the Navy laid down plans for two massive dirigible airships, to be used for long-range sea reconnaissance. These were to be 480 feet long, the longest zeppelins ever built to that time (only the later German passenger airship Hindenburg, at 500 feet, was larger). The Navy zeppelins had eight gasoline-powered engines that could drive them at a cruising speed of 60 mph, with maximum speed of 85 mph. Lift was provided by 12 helium gas cells. They could travel over 10,000 miles without refueling. The first of these airships, named the Akron, was commissioned in 1931. Her sister ship, the Macon, followed in 1933.
The US Navy airship Macon
The Akron and the Macon were not merely dirigibles, however--they were flying aircraft carriers. This idea had been tried before--during World War One, specially modified Sopwith Camels and Curtiss Jennies were strapped to zeppelins and carried aloft. The idea never really worked, however--the most difficult puzzle was how to "land" back at the zeppelin when the mission was over. Most times, the airplane simply flew back to an airfield.
On the Macon and Akron, a different idea was used. Carried inside the cavernous interior of the dirigible's aluminum frame were several specially-designed Curtiss F9C-2 "Sparrowhawk" biplanes. Each plane had a reinforced hook attached to the upper wing. To launch the plane, the crew would attach this hook to a metal contraption called the "trapeze", then lowered the Sparrowhawk through a hatch until it dangled below the airship, where the hook was disengaged and the plane dropped free to fly on its own. While the Sparrowhawk carried machine guns and was capable of defending the airship against enemy planes, its primary task was to increase the reconnaissance area that could be covered by flying around away from the airship. Upon its return, the pilot would carefully maneuver the Sparrowhawk into position underneath the dirigible (much like a modern jet fighter attaching to a refueling tanker) and hook the plane back to the trapeze, which was then drawn inside. On such missions, the Sparrowhawk had its landing gear removed and replaced with an extra gas tank, to save weight and increase its reconnaissance range.
The Akron could carry four Sparrowhawks in her hangar; the Macon could carry five.
A Sparrowhawk inside the Akron's hangar.
Both airships were used in tests to determine how effective they could be in locating ships at sea, and both perfected the logistics of launching and recovering their Sparrowhawk "parasite fighters". Neither one, however, would see service in the wartime role for which they had been designed. The Akron in particular had a troubled history. In February 1932, the ship struck the ground while leaving her hangar in high winds, damaging her tail structure. Three months later, the Akron flew from New Jersey to San Diego on a training mission. When she moored in California, however, the inexperienced Navy ground crew took too long to secure her, and when she inadvertently floated up into the sky, three ground crewmen were still clinging to the mooring lines. Two fell to their deaths; the third hung on for over an hour before being winched aboard the airship.
In April 1933, the Akron encountered severe weather while flying along the Jersey coast and crashed into the ocean, killing 73 of the 76 men aboard.
The Macon was commissioned a month after the Akron crash. Her design had been modified as she was being built, so she had a longer range and could carry an additional Sparrowhawk aircraft. The Macon was eventually commanded by Lt Commander Herbert Wiley--one of the three survivors of the Akron .
In February 1935, the Macon ran into a thunderstorm off the coast of California, broke up, and crashed into the sea near Monterey Bay. This time, only two of the 75 crewmen were killed.
Sparrowhawk attaching itself to the trapeze.
The accidents involving the Akron and Macon, along with the spectacular fire that destroyed the passenger airship Hindenburg, convinced the Navy that large zeppelins were a technology whose time had come and gone. While the Navy would use a number of small blimps for reconnaissance (and still does), large airships would not play a major role again.
During the Second World War, though, the concept of the "parasite fighter" still survived. The Soviet Union experimented with the concept by attaching small I-16 Polikarpov fighters to the wings of its Tupolev TB-3 heavy bombers, and in 1941, I-16's fitted with small bombs and carried by TB-3's were released to attack German targets in Romania, the only instance of parasite planes being used in combat. The Germans, conversely, experimented towards the end of the war with the idea of carrying small jet-powered Me-328 fighters under the wings of heavy bombers, but was unable to make much progress before the war ended.
The most ambitious work was then carried out in the US. In 1946, the successor to the B-29 bomber, the B-36 Peacemaker, began flying. As the primary delivery system for the nuclear bomb, the B-36 was expected to fly all the way from bases in the US to the Soviet Union, a distance that could not be covered by any escort fighters. As a result, it was planned that a number of B-36's would be converted into flying aircraft carriers which could bring their own escort fighters along with them. Thus was born the XF-85 "Goblin", a diminutive little jet fighter that could be carried inside the B-36, lowered on an aerial trapeze to fly off and fight Soviet interceptors, then reattach itself to the trapeze to be hauled back aboard--a carbon copy of the Sparrowhawk mission. About ten percent of the B-36 force was intended to carry a load of three or four Goblins instead of bombs. But problems arose in dealing with the heavy turbulence caused by the B-36's six rear-facing engines, and the Goblin project was cancelled in 1949. Only two of the little jets were built. By this time, the development of workable air-to-air refueling equipment gave jet fighters virtually unlimited range and endurance, and removed the need for bombers to carry their own fighter escorts with them.
Only six F9C-2 Sparrowhawks were built. Four were assigned to the Akron, but none of these were aboard when she crashed. All six were then assigned to the Macon, and four of them were on board when she sank into the ocean. One of the two surviving planes was scrapped in 1937. The last remaining Sparrowhawk was given to the Smithsonian Air and Space Museum in 1940. It is currently on display in the Udvar-Hazy Center.
Curtiss F9C-2 Sparrowhawk on display at the Smithsonian's Udvar-Hazy Center