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The unsuccessful Rheinmetall-Borsig launcher was replaced by a Walter design and the first prototype is seen here during trials in the autumn of 1943. (NARA)

Trials with the new Askania autopilot guidance system began in the summer of 1943. A magnetic compass served as the azimuth control, keeping the missile heading along a predetermined magnetic bearing to the target. A pair of gyroscopes monitored yaw and pitch, while a barometric device monitored the altitude. A small propeller on the nose of the missile was linked to an air-log which measured the distance that the missile had traveled. The autopilot was preset prior to launch regarding the missile's cruising altitude and target range, while the azimuth was determined by the orientation of the launcher. Once the air log had determined that the range had been reached, two detonators fired which caused the rudder and elevators to lock, pushing the missile into a steep dive towards its target. Fieseler boasted that 90 percent of the production missiles would strike within a circle 10km (6 miles) around the target, and that half would land within a circle 6km (3.7 miles) in diameter around the target.

On Hitler's orders, a special commission was convened on May 26th, 1943, to determine whether the Luftwaffe's FZG-76 cruise missile or the Army's A-4 ballistic missile was the preferable bombardment weapon. The commission concluded that both the FZG-76 and A-4 should be manufactured since they were complementary to one another. The FZG-76 was judged to be more vulnerable to interception, but was far less expensive to manufacture and much simpler to operate; the A-4 ballistic missile was invulnerable to interception, but was very expensive to manufacture and complicated to operate. By the late summer of 1943, the Kirschkern had progressed far enough to begin plans for serial production. The original plans called for serial production to begin in August 1943 so that 5,000 missiles would be ready when combat use began on December 15th, 1943.

Flying bomb designations

Among the more confusing aspects of the Fieseler flying bomb were its numerous names and codenames. As mentioned earlier, its early names included the Fieseler designation Fi-103, and the Luftwaffe cover-names FZG-76 and Kirschkern. On April 30th, 1944, Hitler ordered that FZG-76 Kirschkern be dropped in favor of Maikäfer ("June Bug"). This was one of the more short-lived names as the German propaganda ministry started using the term V-1 (VergeUungswaffe-1 - "Retaliation weapon 1") during radio broadcasts on June 23rd, 1944, and Hitler made this its official name on July 4th, 1944. V-1 lasted until November 2nd, 1944, when Hitler renamed it Krahe ("Crow").

Some of the Fi-103s were tested from aircraft, in this case an He-111 of Erprobungskommando Bannock at Karlshagen. This particular missile, FM03V83, was launched on August 22nd, 1943, and inadvertently crashed on Bornholm island. Danish resistance provided pictures of the wreckage to British intelligence, the first detailed glimpse of the new weapon. By this stage, the V-zellen missiles had the improved air intake at the front of the engine but still employed the external yoke mounting. (NARA)

The FZG-76 enters service

In April 1943 Colonel Max Wachtel was appointed to command the first missile unit, Lehr-und-Erpmbungskommando Wachtel ("Wachtel Training and lest Command"). This unit was deployed at the Zempin test range near Peenemünde and another catapult site was built on the Baltic for training. This was the seed for the later combat unit, Flak-Regiment 155 (W), the W indicating Werfer, or "launcher", and not Wachtel as is so often reported.

There was no consensus on how best to deploy the new missiles. The Luftwaffe Flak commander, Lt. Gen. Walther von Axthelm, wanted the missiles deployed in a large number of small field bases that could be easily camouflaged. The head of the Luftwaffe production program, Field Marshal Erhard Milch, favored a small number of large bomb-proof bunkers, a position that was supported by Hitler based on the success of the heavily fortified Brest U-boat shelters in resisting Allied bomber attacks. On June 18th, 1943, Luftwaffe chief Hermann Goring held a meeting with Milch and Axthelm to settle the issue. Goring suggested a compromise: four large missile bunkers would be built, along with 96 field sites. In addition, the launch of FZG-76 missiles from bomber aircraft would also be employed. Production would start in August at a rate of 100 per month, gradually ramping up to 5,000 monthly by May 1944. Goring wanted 50,000 per month, but no sober official treated this seriously. Hitler approved the plan on June 28th, 1943, setting in motion the Kirschkern construction program.

Manufacture of the Fi-103 started months late. Initial production was scheduled to begin at the Volkswagen plant at Fallersleben and at Fieseler in Kassel-Bettenhausen in August 1943. Minister for War Production Albert Speer continued to favor the Army's A-4 missile program, and a Luftwaffe decision to emphasize fighter construction adversely impacted the FZG-76 program since it was considered a bomber-substitute. In some respects, the delay was not entirely unwelcome as the FZG-76 was still not mature. Through August 1943, only 60 percent of the test launches were successful. The early FZG-76 missiles were categorized in three batches, the V-zellen (Vorserienzellen: prototype airframes); M-zellen (Modellserienzellen: pre-production); and G-zellen (Grosserienzellen: serial production). Although 200 V-zellen had been planned, only 120 were actually completed and most had been launched by the end of the summer of 1943. By September 1943, only 38 M-zellen missiles had been delivered, and the first training launch by Wachtel's regiment did not take place until October 26th, 1943. The guidance system was still not mature. In December 1943 British intelligence decrypted the tracking reports from radar stations along the Baltic which revealed that guidance problems were still so severe that, if the FZG-76 had been launched against London as planned in December 1943, fewer than one in six would have landed in the city, even discounting premature crashes and British counter-measures.

This is FM03M23, one of the M-zellen pre-production missiles tested in the fall of 1943. (NARA)

On October 22nd, the RAF raided the Fieseler plant, shutting down its Fi-103 line. Production was further delayed by the endless stream of changes and modifications to the design. The M-zellen missiles were prone to flip over on their backs after launch due to shortcomings in the new guidance system, and the serial production G-zellen were even worse, often losing their wings after launch. The G-zellen problem was traced back to a production change between the pre-series and mass-produced missiles where spot-welding had replaced more time-consuming riveting. The new lightweight stamped-steel wing rib proved too weak and the first batch of 1,400 airframes had to be scrapped. At the end of November production was halted until the problems could be remedied. Significant production did not resume until March 1944 after the production faults had been ironed out. An Allied bombing attack on the Fallersleben plant missed the FZG-76 production line and in July FZG-76 production was started at the notorious underground Mittelwerke plant near Nordhausen since it was less vulnerable to bombing.

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