Staff Writer (Updated: 5/16/2016):
It was not until 1944 that Luftwaffe authorities found the idea practical and launched an official program under the name of "Mistel" ("Mistletoe") to develop a realistic battlefield solution. In the conversion of some 100 Ju 88 bomber airframes, the crew components and defensive armament positions were all stripped from the airframe. A simple strut network was affixed to the dorsal spine of the bomber and, to this, was added the fighter portion. The initial prototype was a Bf 109E-4 fighter over a Junkers Ju 88A model series bomber.
The general idea behind the Mistletoe pairing was providing an impressive war load to a basic frontline fighter. The strut network was fitted with explosive bolts which were detonated when the payload was near the target area. Guidance was from the mothership/carrier aircraft and release was at the discretion of the pilot. Once the bomb load was dropped, the fighter regained nearly all of its fighter-like performance and handling qualities to help defend itself. A bomb load could feature as much as 4,000 pounds of explosive material - enough to cripple a warship, destroy a bridge, or penetrate fortified structures.
There proved a slew of Mistletoe derivatives (some realized and others only planned) including the Bf 109F-4/Ju 88A-4 combination under the name of "Mistel 1". The Mistel S1 was to be its trainer platform as such an aircraft required specific training in the handling and release of the large payload. The "Mistel 2" was born from the pairing of an Fw 190A-8/F-8 fighter variant with the Ju 88G-1 bomber. Its trainer was Mistel S2. The Mistel 3A used the Fw 190A-8 with the Ju 88A-4 and its trainer became Mistel S3A. The "Mistel 3B" involved the Fw 190A-8 with the Ju 88H-4 bomber. The "Mistel 3C" was an offshoot and consisted of the Fw 190F-8 with the Ju 88G-10. The "Mistel Fuhrungsmaschine" paired the Fw 190A-8 and Ju 88A-4/H-4 bombers. The "Mistel 4" was to involve the jet-powered Messerschmitt Me 262 fighter over the Junkers Ju 287 forward-swept wing, jet-powered bomber. The "Mistel 5" incorporated the jet-powered Heinkel He 162 fighter over the Arado E.377A flying bomb.
The Fw 190 was also proposed as a carrier for a bomb-laden Ta 154 fighter and the Arado Ar 234 "Blitz" jet bomber over the Fieseler Fi 103 "Buzz Bomb". Various other forms were envisioned but never made it beyond the paper stage.
The two models to have seen operational service were the Bf 109F-4/Ju 88A-4 and the Fw 190A-8/Ju 88A-4 combinations. Earliest use came during the Battle of Normandy stemming from the Normandy beach landings of June 6th, 1944 (Operation Overlord). They were also used along the East Front against Soviet forces though, in any case, results were decidedly mixed with German pilots claiming direct hits and damaged targets though records from opposing sides indicating otherwise. These exercises more or less meant that the Mistletoe program was a failure considering the amount of manpower and material dedicated to the project.
Total Mistel production ended at about 250 examples.