Operation Oyster was a bombing raid made by the Royal Air Force (RAF) on 6 December 1942 upon the Philips works at Eindhoven in the Netherlands. The Philips company was a big producer of electronic equipment, including vacuum tubes for radio communication. Prior to the Battle of the Netherlands in 1940, Philips was known to be a leading research firm in infrared and radar technology. To ensure accuracy and minimise casualties among the Dutch citizens, the raid had to be undertaken during the day.
Eindhoven was beyond the range of the fighter escort and the four-engined night bombers that made up the bulk of RAF Bomber Command were considered to be too vulnerable for the attack. No. 2 Group RAF contained the medium day bombers of the RAF and was selected for the raid. To improve their chances of survival, diversionary raids were organised to mislead the German defenders. Almost all of 2 Group was committed to the raid and it was the largest and most successful operation by the group of the war.
Background
Philips, Eindhoven
In April 1942 the Air Ministry, in consultation with the Ministry of Economic Warfare, produced a list of the highest value targets in the occupied countries. Eight targets within range of the RAF were identified. The Philips radio and vacuum tube factory in Eindhoven was made the priority target, considered as important as any target in Germany. Philips was a leading firm in electronics and a big employer in Eindhoven, where production was performed at the massive Strijp works, and the smaller Emmasingel works, half a mile away to the south-east.
Prior to the war Philips made major advances in the design and production of vacuum tubes and had some of the best research scientists in the world. An appraisal by the Air Ministry estimated that the plants in Eindhoven produced a third of the radio tubes used in German military equipment. It was feared that the firm was being used to perform research into electronic counter-measures and radar technology.
The location of the Philips works in the middle of a Dutch city precluded Bomber Command from putting on a big night raid, as this would result in a great many civilian casualties. For accurate bombing the target would have to be attacked during the day. The raid resulted in about 150 civilian casualties. Being 70 mi (110 km) inland, Eindhoven was beyond the range of fighter escort. Using Lancaster bombers for the raid was considered and rejected, as they were too vulnerable to fly through the middle of the German fighter belt in daylight. The use of de Havilland Mosquitos was also considered but the Philips works was too large a target for the payload the Mosquitos available could carry.
2 Group
No. 2 Group RAF was the sole day bomber group of RAF Bomber Command and consisted of ten medium bomber squadrons stationed on airfields in Norfolk. The group flew with Fighter Command in operations against the Luftwaffe. Daylight raids with small formations attacked shipping, targets on the coast and in northern France. The raids were flown at medium altitudes through the German fighter defences but the two large Philips plants in Eindhoven could not be destroyed by the typical twelve-aircraft formations used in Circus raids. Bomber Command elected to commit all ten squadrons of 2 Group to the raid but this meant using four types of medium bomber; the Lockheed Ventura, Douglas Boston, North American B-25 Mitchell and de Havilland Mosquito, with inconsistent performances. It was the most ambitious raid ever put on by 2 Group and approval for the raid was given on 9 November 1942 as Operation Oyster.
Prelude
Training
The first full scale practice was held on 17 November. The Ventura crews soon learned that the backwash off the paddled blades of the other Venturas made their planes liable to skid and difficult to control; flying so low left no time for recovery. Any mistake they made could quickly lead to them flying into the North Sea or the ground. The pilot had to be very attentive to stay on station, focused on the wing or tail of the aircraft before him. The lead pilot had to be aware of the trailing aircraft, accounting for their position with each manoeuvre he made. While flying low over Holland the pilots and navigators would have to keep a sharp eye out for obstructions. Birds on the coast tended to be larger, and when startled by the noise of an aircraft engine they would take off into the air. The risk of bird strikes was one of 2 Group's greatest dangers.
The initial plan was for the Venturas to attack first, followed by Bostons at one target and Mitchells and Mosquitos at the other. All aircraft would fly at low level until right before the target, when they would climb to 1,500 ft (460 m) to attack in a shallow dive. The first trial was disappointing, aircraft arrived over the target from different directions and at different times. The Venturas arrived over the target in a ragged fashion. It was apparent that time was needed for the aircraft to form up into groups by type. It was also apparent the Mitchell crews were simply not ready to fly a raid this demanding in air discipline. It was realised that if the Venturas attacked first with incendiaries, smoke from the fires they started would obscure the target for the following aircraft.
The order of the attacking aircraft was changed, the Bostons to attack first, followed by the Mitchells and Mosquitos, with the Venturas arriving last. Take-off times were also pushed forward to allow the aircraft more time to orbit and form up. A second trial run by the Venturas the next day was much better. Between exercises crews practised bombing at low level, 1,000 ft (300 m) and 1,500 ft (460 m) in all manner of formations in pairs and combinations of three pairs. A third trial run with all forces on 20 November was much better but the Mitchell squadrons, 98 and 180, were removed from the raid as their crews were still too inexperienced. This brought the force down to eight squadrons.
Plan
The order for the attack and initial plan were issued 17 November 1942. Training for the raid began immediately. Wing Commander James Pelly-Fry of 88 Squadron was chosen to lead the attack. He was an experienced pilot who had flown in Africa and been in command of 88 Squadron since the start of the year. Pelly was to fly one of the two low level lead Bostons against the Emmasingel factory, and would be the first man to the target. Circus raids by 2 Group involved from six to 30 bombers, flying at medium altitudes and rendezvousing with their fighter escorts on the way. To strike with the element of surprise, the Eindhoven raid was to be flown at low level from start to finish. Low level flight would avoid radar detection, limit the exposure to anti-aircraft fire and make it more difficult for German fighters to attack.
None of the crews had experience flying a mission in such a large formation, nor so low to the ground. The four types of bombers being used had different ranges and different top speeds. To overwhelm the defences at the target and limit losses it was planned that all aircraft would be over the target, deliver their bombs and be gone in ten minutes. The Venturas were the slowest, the Bostons and Mitchells intermediate and the Mosquitos the fastest. The plan was based on the constraints of the performance of the Venturas, which would be operating close to their maximum range at Eindhoven. The aircraft were to fly in pairs, in echelon formation to starboard. As many as six aircraft could be grouped but no more as formation flying was awkward and made it difficult for any kind of manoeuvre. The big problem was getting a large group of aircraft to arrive at precise times. Formation flying was not new to the group but large formation flying at tree top level was. The attacking force was made up of 48 Venturas from 21 Squadron, 464 (Australian) Squadron and 487 (New Zealand) Squadron, 36 Bostons from 88 Squadron, 107 Squadron and 226 Squadron and ten Mosquitos from 105 and 139 Squadrons.
Though different speed ranges were assigned to the aircraft based on type, all aircraft were to approach, attack and leave the target at their maximum speed. Twelve Bostons, ten Mosquitos and thirty-one Venturas were to strike the main target at the Strijp Group works as twenty-four Bostons and seventeen Venturas attacked the Emmasingel radio tube factory half a mile to the south-east of the main complex. The Boston and Mosquito bombers would carry four 500 lb (230 kg) high explosive bombs, fuzed for 0.025 seconds delay to minimise the tendency for the bombs to slide away from the target before exploding.
Once the aircraft had released their bombs they were to hedge-hop home at full speed. It was decided after the third trial that a Boston from each squadron would fly at low level all the way to the target to draw the attention of German Flak gunners down and away from the larger force that was climbing up to 1,500 ft (460 m) behind them. The low flyers' four 500 lb (230 kg) bombs were to be fused for eleven seconds delay to prevent the aircraft from being caught in the explosions. The Venturas following them would each carry forty 30 lb (14 kg) incendiary bombs and two 250 lb (110 kg) high explosive bombs. The incendiaries were phosphorus, which would stick to whatever they struck and burn. The two 250 lb (110 kg) high explosive bombs on the Venturas were to be fuzed for 30 or 60 minutes' delay, to hamper or injure the firefighters and rescue workers.
The Mosquitos would follow the Bostons on the same route, while the Venturas were to fly slightly to the south before turning towards Eindhoven. The three groups were to arrive over the target in close succession. The attack was to be concluded within the span of 10 minutes. The Bostons were to release bombs at zero hour, which was set for 12:30 p.m. They were to be followed by the Mosquitos at zero plus 2 minutes and the Venturas would drop their bombs and incendiaries at zero plus 6 minutes. The Venturas were to turn west after they had bombed; the Bostons were to fly north for 2 mi (3.2 km) and then turn west, so that both groups would arrive over the coast simultaneously. The Mosquitos were generally to fly north initially but were not bound to the other aircraft for the return trip.
Spitfires from No. 12 Group RAF were to escort the bombers home from the coast and as far as 5 mi (8.0 km) inland. Further efforts to protect the bombers involved diversionary raids by the United States Army Air Forces (USAAF), with a formation of Consolidated B-24 Liberator heavy bombers sent to the German airbase at Abbeville, and a larger formation of Boeing B-17 Flying Fortresses sent to Lille, with Spitfire escorts. Eight North American P-51 Mustang fighters of 268 Squadron were to undertake a "Rhubarb" (ground strafing attack) near Alkmaar in North Holland. On the evening of Wednesday, 2 December, the crews were briefed on the raid; no-one was allowed to enter or leave the air bases, no mail was allowed out and the telephones were guarded. The next morning, Thursday 3 December, the RAF Meteorological office declared weather conditions were unsuitable. The stations remained closed as the crews waited for the weather to improve. Finally on Sunday 6 December the weather over Eindhoven was declared favourable.
Diversionary raids
The day started with the Eighth Air Force launching its diversionary raids; nineteen B-24s from the 44th Bomb Group were sent out at 9:30 a.m. to attack the German airfield at Abbeville. An hour later the primary effort of 66 B-17s from the 91st, 303rd and 305th Bomb Groups were aloft to bomb the Atelier d'Hellemmes rail yard at Lille. During these operations the Eighth Air Force used replacement crews to fly two mock runs over the channel to divert attention from the main effort, the diversions looking like routine operations.
The US bomber groups were detected and followed by German air controllers. Luftwaffe fighter aircraft from JG 1, JG 26 and JG 2 were sent up to intercept them. En route to Abbeville the B-24s of the 44th were recalled but one flight of six aircraft did not receive the message and continued. This flight was intercepted over the target and lost one of their B-24s but they reached the airfield, dropping their bombs at 11:24 a.m. Thirty-five minutes later the main force of B-17s rendezvoused with their Spitfire escorts, arrived over Lille and bombed the rail works at 12:10 p.m. Thirty-seven of the US bombers were considered effective on target. As they were exiting the target area they were attacked by 20 to 30 enemy aircraft, losing one of their number.