The stand-off probe was necessary to set off the main explosive charge at the optimum distance from the target, so that the soft metal liner had time to form itself into a thin jet before it struck. Within limits, the further the charge from the target when it was detonated, the thinner and deeper the hole "drilled"; the closer the charge to the target, the wider and shallower the penetration. Both long and short stand- off probes were used with the Mistel. The entire hollow-charge action took place within one ten-thousandth part of a second, during which time a relatively slow-moving Ju 88 explosive aircraft, impacting at 400 m.p.h., moved forwards about a half an inch. This, then, was the potential of the Mistel device.

The Ju 88 used for the Mistel program had their crew compartments removed at the after bulkhead, then these were re-fitted in place by means of quick-release fasteners. For ferry and training flights both the upper and the lower components were manned. At the last possible moment before an attack, the crew compartment was removed for the last time and the deadly hollow-charge warhead fitted in its place. This task required six mechanics, two armourers, and four ton capacity crane, and took one day. The process had an air of finality about it, for once the warhead-fitted Mistel had taken off the fighter pilot could not land the combination; whether it reached the target or not, the Ju 88 lower component was doomed. A series of aiming tests against cliffs on the Danish island of Moen proved the feasibility of the weapon.

TRAINING

Mistel pilots began training in April 1944, using the first two prototypes. Each man completed ten flights without releasing the lower component, then three flights each with a release. The pilots found that the poor view forwards from the fighter cockpit made the initial part of the take-off run difficult, and this ruled out the possibility of night take-offs. However, once it was airborne they found the Mistel easy to fly, if a little sluggish on the controls.

Mistel combinations were put together using a number of different types. The original employed the Bf 109F and the Ju 88A, later ones employed various sub-types of the Fw 190 and the Ju 88. Versions projected but never assembled comprised an Me- 262 jet fighter on top of a Ju 287jetwmber, and an He 162 jet fighter mounted on an Arado E 377 A flying bomb. 

IN ACTION

The first unit to receive the Mistel was the Second Staffel of K.G. 101, commanded by Captain Horst Rudat. But before Rudat could move his Staffel to Grove things had come to the boil in France, for on the June 6 Allied forces had landed in Normandy. Accordingly, the few Mistel combinations available were ferried to St Dizier in France, for operations against the invasion fleet. The Mistel pilots did claim some hits, but none of these are confirmed in Allied records. An explanation for this could be that some of the hits were on the old French battleship Courbet, which was being used as a block ship for the British "Mulberry" harbour at Courseulles. Since the ship was already lying on the sea bottom, in shallow water, the Royal Navy were more than happy to have the Germans attack her in preference to more worthwhile targets. So Courbet was dressed up to look as conspicuous as possible, with an enormous tricolour complete with the cross of Louraine; thereafter she acted as a magnet for attacks. She certainly collected several bombs and torpedoes, and possibly a Mistel or two. 

In the autumn of 1944 the plan for the Mistel attack on Scapa Flow was suggested for the second time, and composites flew into Grove and neighbouring Danish airfields in readiness. But the Royal Air Force struck first, and set in train a pattern of events which brought the carefully-laid German plan to nothing.

On the November 11,1944 Lancasters attacked the German battleship Tirpitz with 12,000 pound Tallboy bombs, and caused her to capsize. With Tirpitz out of the way there was no call for battleships or fleet aircraft carriers to be held in the Atlantic, and within weeks those which had served with the Home Fleet at Scapa Flow were on their way to the Pacific. This meant all the worthwhile targets had left Scapa Flow. The combinations would have to be used elsewhere.  

THE "IRON HAMMER" PLAN

"Operation Iron Hammer", the planned blow to knock-out the Russian armament industry, had first been mooted at the end of 1943. The key targets within Moscow and Gorky were judged to be the steam and hydro-electric generating stations.  It was known that the Russians lacked the plant to produce such turbines - most of the equipment scheduled for attack under the "Iron Hammer" plan had been supplied by the Germans before the war. As a result the Luftwaffe planners felt that the Russians would not be able to effect repairs for a very long time. But before the plan could be put into action the Russians overran the advanced bases which were to have been used. Now the targets lay beyond the range of the He 111.

The idea of the knock-out blow was revived in December 1944, when the plan was expanded in scope and re-scheduled for the spring of 1945, this time using Mistel combinations. The operation's supporters believed that such a powerful blow from the supposedly dying German Air Force would come as a great shock to the Russians, and might well have the useful secondary effect of causing them to pull back fighter units for home defense.

Despite the deep penetration necessary to reach the "Iron Hammer" targets, the German planning staff felt that the operation had a good chance of success. Since the autumn of 1943 German bomber activity over rear areas in the east had been negligible, and as a result the Russian home air defenses were weak and underdeveloped. The only German unit to fly regular missions over Russia since then had been KG 200, which was engaged in dropping and supplying agents. The unit's aircraft had regularly carried radar observers, and as a result the Germans knew that the radar cover in the rear areas was thin. Since the targets were both large and ill-defended, a night attack using flares was judged feasible.

For the operation specially modified Mistel combinations were prepared, able to cover the 760 mile distance from the base airfields to the targets. The Fw 190 upper components were each to carry two drop tanks for fuel, and additional tanks for both fuel and oil. Following tests held at Udetfeld with the warhead, it was calculated that two hits with hollow- charge fitted Ju 88's would be sufficient against the smaller power stations, while six hits would be necessary against the larger ones.

The revived plan had intended that the Mistel combinations should take off from airfields in East Prussia; later, as the front line had moved back with disconcerting speed during the Russian offensives in January and February, 1945, the operation was re- planned to use airfields at Oranienburg, Parchim, Laertz, Marienehe and Peenemünde. The return flights were to be either to the home bases or else to airfields in the Courland Peninsular pocket, depending upon fuel and weather conditions.

Lieutenant Colonel Werner Baumbach was made responsible for the execution of the Iron Hammer operation. Under his control were the Mistel combinations of K.G. 30 and K.G. 200, as well as a number of He 111.'s, Ju 88's and Ju 290's which were to act as route and target markers during the attack. However, by the time sufficient Mistel combinations were available, such as the Mistel 2 shown above, there were other tasks for which they could be used. For by March 1945, the Russians were streaming westwards over the Vistula bridges. Something of the dilemma that faced the Germans may be sensed from a conversation held between Hitler and General Karl Koller, the Luftwaffe Chief of Staff, on March 26,1945:

Koller: Altogether there are 82 Mistel combinations ready for use. If the urgent attacks on the Vistula bridges are carried out as you, my Führer, have commanded Lieutenant Colonel Baumbach, there will remain 56 combinations for the "Iron Hammer" operation. Since the report from General Christian would you not prefer that we carry through a smaller "Iron Hammer" with these 56 Mistels? I wish to propose that as well as the urgent Vistula bridge attacks, the "Iron Hammer" operation should be carried through with these 56 Mistel combinations. The attack on the Gorky group of targets would then have to be omitted. We should then knock out 80 per-cent of their electrical generating capacity; of their 1,094 million kilowatts ,the reduction would be only 378 million kilowatts. I ask therefore that the proposed "Iron Hammer" operation be approved; technically we can be completely ready by the 28th/29th, provided the weather conditions are favorable.
Hitler: I do not wish to divide the effort, because when we do it a second time the enemy will be ready, and will reply with strong defensive measures.
Koller: Naturally it would be a shame if the complete "Iron Hammer" operation could not be flown, but I do not know when we could ever do it again; the earliest that it could be done again is during the next moon period. I should also like to believe that the range of the targets is such that strong defenses will not be met, because presumably the enemy will not expect us to attack over such great distances.
Hitler: Nevertheless, one knows how significant it would have been if the enemy had attacked our power stations simultaneously. It is exactly the same with the enemy. For the present I prefer to give up the Vistula Bridge attacks; that can be done later.
Koller: So the "Iron Hammer" operation can be carried out in full with no diversion of effort for the Vistula Bridge attacks?

The transcript ended: "The Führer agreed with this." But the "Iron Hammer" operation was not to be mounted on the March 28. Shortly after the conversation it became clear that the bridge attacks could not be "done later". The Russians were massing for a   breakthrough along the line of the Oder River where for the time being they were held, though in places less than 35 miles from Berlin itself. At Küstrin they had already established a bridgehead on the west bank which had resisted all German attempts to throw it back. When the Russian attack came, there could be no doubt that the crossings at Küstrin would playa major part in it; accordingly, the carefully husbanded stock of Mistel combinations was sent in to smash them.  

THE ODER BRIDGE ATTACKS

In charge of the Oder bridge attacks was Colonel Hans-Joachim Helbig. This use of Mistel combinations against bridges was a measure of desperation, for although they were potentially a very effective weapons against ships or concrete buildings whose walls would contain some of the force of the explosion, they were quite unsuitable for this task. Not only was the accuracy of the Mistel inadequate for use, against such long narrow targets, but the specialized warheads merely blew holes through the bridges without damaging any vital part of the structure.

Typical of the attacks on the bridges at Küstrin was that on April 12, 1945. At 1825 hours that evening Second Lieutenant Hans Altrogge took off from Peenemünde in a Ju 88 of I/jK.G. 66, to act as lead aircraft for the attack. Four Mistel combinations followed him into the air, and the curious formation headed south towards the target. The view from the upper component Fw 190's was not good, and the Ju 88 pathfinder flew some two miles in front and 1,500 feet above the combinations, so as to stay in sight. It was dusk when Altrogge arrived at Küstrin. When overhead the bridges he rocked his wings then climbed away; this was the cue for the Mistel pilots to push their aircraft down and go straight into the attack. In the face of heavy anti-aircraft fire the pilots pressed home their dives, separated, then pulled away.

The salvo of explosive Ju 88's continued on, and from his vantage point Altrogge watched the bridges disappear in a cloud of smoke, mud and spray. Freed of their burdens the Fw 190's became potent fighters once again, and now vengefully curved in to strafe the flak pits which had made things so hot for them during the attack run. Before the smoke cleared it was dark, and Altrogge was unable to observe the results of the strike. But from Russian records we know that the bridges continued in use after the attack. The Küstrin bridges were of the simple pontoon type, erected by Soviet army engineers; pontoons are easy to replace. The Russians launched their great offensive on April 16, and within two days had forced two bridge- heads, one 20 miles wide and one 30 miles wide, on the western bank of the Oder. More and more pontoon bridges were thrown across the river, and the Luftwaffe used everything it had, including Mistels and Hs 293 glider bombs, in an attempt to smash them. But such was the force of the Russian push that even when some of the crossings were temporarily put out of action the drive was not slackened in the least.

When the war ended, in May 1945, the Mistel had achieved none of its spectacular promise. Potentially the weapon was capable of a great deal. For example, had a dozen or so combinations penetrated the defenses and reached the anchorage at Scapa Flow, they could well have disabled the entire battleship and aircraft carrier strength of the British Home Fleet. Had a blow been synchronized with a sortie by the German battleship Tirpitz - assuming that Tirpitz could have been made serviceable following the damaging attacks by aircraft and midget submarines - severe disruption to Britain's Atlantic lifeline might have resulted. But by the middle of September 1944 it was already too late. The cumulative damage suffered by Tirpitz had rendered her unfit for sea; she was retained in service merely to keep Allied warships tied down. A successful Mistel attack in November 1944 would have inflicted a severe blow on British morale, but would have achieved little else; the battleships and fleet carriers of the Home Fleet took no part in the closing months of the European war anyway. So when the Mistel was ready for action in sufficient numbers, the important issues had already been decided. It was the same with the "Iron Hammer" plan. Had the operation been successfully mounted in 1944 the mighty Russian advance might well have been forced to a halt for want of supplies. But by the early part of 1945 it was too late for such an attack to make much impression; the Russian forces could have continued on pretty much as they did, using munitions already manufactured.

MISTEL VARIANTS
Mistel 1 Ju 88A-4 and Bf 109F-4
Mistel 2 Ju 88G-l and Fw 190A-8 or F-8
Mistel 3A Ju 88A-4 and Fw 190A-8
Mistel 3B Ju 88H-4 and Fw 190A-8
Mistel 3C Ju 88G-10 and Fw 190F-8
Mistel 4 Ju 287 and Me 262. 
Mistel 5 Arado E 377A and He 162.

Main additional components fitted during conversion to the Mistel role: 
Patin three-axis autopilot, as modified by Junkers, to the Ju 88. 
Zeise optical sight, to the upper component. Connecting frame, to the lower component. Additional engine instruments mounted on the outside of the engines of the lower component, so that the pilot above could observe engine temperatures, boost pressures, etc. 
7,800 pound hollow-charge warhead, containing 3,800 pounds of explosive (70 per-cent hexogen and 30 per-cent TNT). Impact fused, arming took place about three seconds after separation

References

"Squadron/Signal Junkers Ju88 in Action Part 2"  by Brian Filley with Don Greer, Perry Manely and Joe Sewell
"German Air Force Bombers of World War Two - Vol. 2" by Alfred Price