In May 1916 a Bristol Scout was carried to a height of 1,000 ft (305 m) on the centre-section of a Porte Baby flying boat, to test the feasibility of carrying a fighter to within firing range of the German Zeppelins which were carrying out raids on England. Twenty-two years later Short Brothers flew their Mayo composite, the lower component being a four- engine flying-boat which was used to carry a heavily laden four-engine seaplane aloft with a greater load than the seaplane could have lifted off the water, thereby increasing the seaplane's range.

About the Mistel

The Mistel series of composite aircraft are without a doubt one of the strangest concepts to achieve operational status with the Luftwaffe. The original concept was proposed to the RLM in 1941 by Siegfried Holzbauer, Junkers aircraft's chief test pilot. His idea was to make use of time-expired Junkers Ju 88 airframes be converted to pilotless missiles by the installation of a warhead packed with explosives. One of these would then be flown to within range of a target, controlled by the pilot of a single-engine fighter which was mounted on struts above the bomber's centre section. The fighter would release the Ju 88 and then guide it to the target.
Feasibility test of the new device began in 1942 with the flight of a Klemm Kl 35 fixed on top of a DFS 230 glider towed by a Ju 52. Combinations of Bf 109 E and DFS 230 A were successfully tested.
A prototype combination Ju 88 A-4/ Me 109 E was first flown in July 1943 and found to be practicable; this proved sufficiently successful for Junkers to be contracted to convert 15 Ju 88A airframes to Mistel (mistletoe) configuration, as it was called, presumably to imply its parasitic connection; the programme was codenamed 'Beethoven'. An initial batch of trainers was converted, using Bf 109F-4s as the upper component. The lower component was stripped of nonessential equipment but retained a two-crew layout for training. The nose section could be completely removed by quick-release bolts and an 8,378 lbs (3800 kg) warhead attached.
Operational flying began in mid-1944 when four Allied ships were attacked at night, all being hit but not sunk. Encouraged by these results, the Luftwaffe ordered a further 75 Ju 88G-1 fighters to be converted, this time with Focke-Wulf Fw 190A-6 or Fw 190F-S fighters as the upper components of what became the Mistel 2 composite. Unfortunately, the combination of the Ju 88G with full fuel load and warhead, plus the Fw 190, meant that the lower component was considerably overloaded and burst tires caused a number of take-off accidents.
Several designations resulted from different combinations of fighter and bomber:

A-Operational

B-Projected

Plans for a night attack on the British Fleet in Scapa Flow by 60 Mistel combinations, in December 1944, were thwarted by bad weather. The aircraft were unable to leave their Danish bases, perhaps fortunately for the Luftwaffe, since the combination was only capable of an airspeed of 236 mph (380 km/h) and was so ungainly, the group would have probably been decimated by British night-fighters. The next assault was to be against Soviet arms factories, with a planned date during March 1945. A total of 125 Mistel were then on order, of which 100 were required for this operation, which had to be cancelled when advancing Soviet troops occupied the airfields which were to have been used.

Sporadic attacks were made against bridges on the Eastern and Western Fronts, but the Mistel suffered heavy losses. Development continued, however, including the use of new Ju 88G-10 and Ju 88H-4 airframes on the production line. The Ju 88G-10s were twinned with Fw 190A-8s with overwing long range tanks as Mistel 3C aircraft, while the Ju 88H- 4/Fw 190A-8 composite became the Mistel 3B. A different role was served by a modified Mistel 3B where the lower component with a crew of three became an ultra long-range pathfinder, carrying its own Fw 190A-8 escort as the upper component, for launch only in emergency.

Next generation

This was projected around the fastest available aircraft. Arado designed a gliding bomb to be launched from an Arado Ar 234C, called E 377. This device was so big that it had to be carried into the air in a Mistel configuration. A detachable five wheeled take-off trolley, built by Rheinmetall-Borsig, was used for taking off. The idea was to use warheads of 3969 lb., 4410 lb., and 770 lb., the latter being a hollow charge designed for anti-ship role.
The version E 377 a consisted of addition of two BMW 003 A turbojets to the E 377. A Heinkel He 162 was intended for use as guide aircraft.

Several designations resulted from different combinations of fighter and bomber:

Besides the already mentioned composites of Ar 377 with He 162 or with Ar 234 C, there was a project of mating two Messserschmitt Me 262 A. The lower fitted with a warhead in the nose and with pilot's place occupied by an extra fuel tank. The command aircraft could be a Me 262 A1a series or the sophisticated bombing version, the two seater Me 262 A2 /U2. This last existed only in two prototypes( V 484 and V 555), with slightly different glazing, by the end of the war. The new wooden nose and upper panel ( known as "bomberkanzel", bomber nose) was designed to carry a bomb aimer, who coordinated the drop of the weapon operating a Lotfe 7 bombsight.
Three different versions of the lower component ( or "Grossbombe", big bomb ) were proposed, Ausfuhrung A,B and C. Version A was to have an armoured fuselage nose with liquid explosive, Version B was to have the forward fuselage formed of solid explosive with similar materials in other fuselage areas, and Version C was to have the forward fuselage of version B but with liquid explosive in the other areas.
The combination was to take off on a purpose-built five-wheeled trolley developed by Rheinmetall-Borsig, which was boosted by a Walter HWK 109-501 rocket.

A reconstruction of the center structure was necessary, to fix the "Starthilferegrat" ( booster) to the trolley. A break parachute was placed on the front of the Walter unit. The rest of the trolley was similar to the Ar 234/He 162 and E377/E377a ones.
After the combination had taken off and the rockets had burnt out, the trolley was jettisoned.

Two Me 262 were delivered for conversion as Mistel 4 during December 1944 but, as far as known, the composite never flew before the end of the war. The flight qualities of the composite can be speculated only, because specials problems may have occurred on the handling of four jets at the same time.

We can read more about this matter in an excellent web site devoted to WWII German prototypes www.luft46.com 

Mistel 4 article > Here