This was a US glider bomb raid on Köln (28 May 1944).
Under the command of Brigadier General Robert F. Travis, commander of the 41st Combat Bombardment Wing within Lieutenant General James H. Doolittle’s VIII Bomber Command, the raid was flown by 59 Boeing B-17 Flying Fortress heavy bombers including 19 aircraft of Colonel Kermit D. Stevens’s 303rd Bombardment Group (Heavy). The 59 aircraft involved carried a total of 113 XM108 (Aeronca GB-1) glide bombs against the Eifeltor marshalling yards at Köln.
The GB-1 was the first US glide bomb of World War II, and was a 1,000- or 2,000-lb (454- or 907-kg) HE bomb without its tail unit but fitted with a wooden wing spanning 12 ft 0 in (3.66 m) and carrying a pair of booms which extended to the rear to carry a tail unit with a single horizontal and twin vertical surfaces. The weapon was gyroscopically stabilised and had an autopilot to activate the electric motors which powered conventional control surfaces. With the 2,000-lb (907-kg) bomb, the GB-1 weighed 2,456 lb (1114 kg), and glided at about 230 mph (370 km/h). Dropped at 15,000 ft (4570 m), the GB-1 had a range of about 20 miles (32 km) to impact with the ground, which gave it a significant stand-off capability and made it possible for the launch aircraft to attack without having to overfly the densest concentrations of Flak around major targets.
In September 1943 all was ready for the weapon to be used in anger, and 40 B-17E aircraft, each modified to carry two GB-1 weapons below its inner wing panels, arrived in England on 29 September for the use of the 41st Combat Bombardment Wing.
Senior officers then decided that although the weapon did possess the required stand-off capability, it lacked the accuracy which was needed for daylight raids. By this time its was the Luftwaffe’s fighters rather than Flak which was the main treat to the aircraft of the VIII Bomber Command, and the use of stand-off weapons to avoid Flak seemed less important. Thus the GB-1 concept was shelved.
By a time early in 1944, the Luftwaffe’s fighter arm had been reduced to a shadow of its earlier self, so the moment seemed opportune for the operational use of the GB-1. The first 'Grapefruit' (i) effort was made on 26 April, but the aircraft were recalled because of adverse weather over the European continent.
On 28 May, the 41st Combat Bombardment Wing launched 59 aircraft against the Eifeltor marshalling yards. The weather was good, and the target was visible from the required stand-off range. Cruising at an altitude of 19,500 ft (5945 m) and a speed of 140 mph (225 km/h), from 13,08 some 54 B-17 bombers entered shallow dives to accelerate to 190 mph (305 km/h) while losing between 1,000 and 1,500 ft (305 and 460 m) in a time of 90 to 120 seconds, and then released 108 GB-1 weapons at a distance of 18 miles (29 km) from the target. Once the GB-1 weapons had been released, the bombers turned to port and reassembled at 19,000 ft (5790 m) before returning to base at Molesworth without suffering any losses.
The result of the attack was disappointing, for the GB-1 revealed poor accuracy: many of the weapons failed as their batteries discharged during the attack glide and, bereft of gyro stabilisation, crashed. Only a few of the weapon impacted anywhere near the marshalling yards. Many drifted far off target or glided more or less sharply than the bombardiers had wanted.
Thus while some of the weapons failed as a result of flat batteries, many landed in Köln, causing much confusion, some damage and a number of German casualties. Though the mission was deemed a failure and the experiment with this particular weapon system abandoned, much information was gathered for the development of future stand-off weapons.