'Catechism' was the British sinking of the German battleship Tirpitz by bombing attack (12 November 1944).

The attack brought to an end a long series of British air and naval operations against Tirpitz, whose very existence as a potent warship posed a major threat to Allied shipping and prevented the redeployment of major British warships to other theatres. The battleship had been moved to the Tromsø area in October 1944 after being severely damaged on 15 September during 'Paravane'. This attack had been carried out by the RAF’s Nos 9 and 617 Squadrons, which then unsuccessfully attempted to hit Tirpitz again at Tromsø on 29 October in 'Obviate'.

'Catechism' was a repetition of 'Obviate', and was conducted by the same squadrons. The aircraft departed from bases in northern Scotland and, as a result of clear weather, the British and commonwealth airmen were able to target and bomb the battleship with considerable accuracy. The bombers were not hindered by German warplanes as German fighter units had not taken off in time from nearby Tromsø, but one bomber was significantly damaged by Flak fire.

Tirpitz capsized within minutes of being hit, and while rescue efforts were successful in recovering hundreds of her crew from the water, few of those trapped within the hull were saved. after the attack, several German personnel were convicted of dereliction of duty.

From a time early in 1942, Tirpitz had posed a significant threat to the Allied convoys transporting supplies through the Norwegian Sea to the USSR, and there also remained the possibility that the battleship might sortie from Norwegian waters to attack the transatlantic convoys deemed essential to the survival of the UK. To counter this double threat, the Allies needed to keep a powerful force of warships with the British Home Fleet, and capital ships accompanied most convoys part of the way to the USSR.

Tirpitz was repeatedly attacked by British forces over several years. RAF heavy bombers made four unsuccessful raids on the battleship between January and April 1942 while she was based in the Fættenfjord. From March 1943, Tirpitz was based in the Kåfjord in the far north of Norway. During 'Source' on 22 September, she was severely damaged by explosives placed on her hull by Royal Navy personnel who had used midget submarines to penetrate the Kåfjord. On 3 April 1944, aircraft flying from British aircraft carriers attacked Tirpitz in 'Tungsten' and inflicted further damage. A series of later aircraft carrier attacks were unsuccessful, these attacks including 'Mascot' on 17 July and 'Goodwood' (ii) between 22 and 29 August 1944.

After the failure of 'Goodwood' (ii), it was decided that further carrier attacks on Tirpitz would be fruitless as the Fleet Air Arm’s aircraft were incapable of carrying the heavy bombs needed to penetrate the German ship’s armour. The task of sinking Tirpitz was therefore transferred to RAF Bomber Command. On 15 September 1944, Nos 9 and 617 Squadrons attacked the battleship in the Kåfjord in 'Paravane'. The attack was made by Avro Lancaster four-engined heavy bombers armed with 12,000-lb (5443-kg) Tallboy heavy bombs and 'Johnnie Walker' (commonly called 'JW') motorised mines, the latter designed for air dropping to land in water and then move through the water by rapidly diving and surfacing until they struck their target. When dropped from a high altitude, the Tallboy bomb could penetrate a battleship’s deck armour before exploding within the vessel. Tirpitz was struck by a single Tallboy during the attack and suffered extensive damage to her bow and left her unfit for combat.

As Tirpitz could not be repaired and Soviet forces were advancing toward the Kåfjord, Grossadmiral Karl Dönitz, commander-in-chief of the German navy, ordered that the battleship be transferred to an anchorage near the northern Norwegian city of Tromsø and used as an immobile battery to defend the area from attack. Dönitz hoped that this would also convince the Allies that Tirpitz continued to pose an offensive threat. The anchorage selected lay just off the coast of the island of Håkøya, where it was believed the water was shallow enough to prevent the battleship from sinking but merely settle on the bottom if another attack was successful. Tirpitz arrived there on 16 October. The depth of the water at the mooring was found to be greater than anticipated, leaving the battleship vulnerable to capsizing. Because of the area needed to deploy Tirpitz's anti-torpedo nets, it was not possible to move her closer to shore.

RAF and Royal Navy reconnaissance aircraft located Tirpitz at Tromsø on 18 October. As the Allied intelligence services had not been able to confirm that the battleship had been crippled, it was considered necessary to conduct further air raids, and on 29 October Nos 9 and 617 Squadrons attacked Tirpitz in 'Obviate'. As the Tromsø area was within range of RAF bases in northern Scotland with modified Lancaster bombers, this attack was somewhat simpler to conduct than 'Paravane'. To extend their range, the Lancaster bombers were fitted with extra fuel tanks and more powerful engines, and their forward and dorsal gun turrets and the pilots' armour plate were removed. The reduction in defensive armament left the Lancaster bombers very vulnerable to German fighter aircraft, but they would have to fly without escort as no British fighters had the range needed to reach Tromsø.

During 'Obviate', the bombers flew to the north over the Norwegian Sea, and assembled over Torneträsk lake in northern Sweden. This violated Sweden’s neutrality, but allowed the bombers to approach Tromsø from the south-east, a direction which, the British believed, the Germans would not expect. Despite clear weather for most of the flight, Tirpitz was covered by cloud shortly before the bombers reached the point at which they were to drop their Tallboy bombs. This made it impossible to target the battleship with the required accuracy, and the 33 aircraft which bombed achieved no hits, although Tirpitz was slightly damaged by a near miss. One of the bombers had to make a forced landing in Sweden after being damaged by anti-aircraft gunfire, and the remainder returned to base.

The British remained determined to sink Tirpitz as soon as possible, and preparations for another attack began shortly after 'Obviate'. A report issued by the Royal Navy’s Naval Intelligence Division on 3 November judged that it remained necessary to attack Tirpitz in northern Norway, and argued that the battleship could possibly be repaired and made fully operational if she was left unmolested and able to reach a major port. As it would be difficult to target the battleship during the period of near perpetual darkness in the northern winter, further attacks needed to be made within the 23 days left before the light failed. The RAF’s No. 5 Group directed on 3 November that the next attack on Tirpitz was to take place on 5 November as 'Catechism', which was to take the form of a rerun of 'Obviate'.

Two de Havilland Mosquito twin-engined meteorological reconnaissance aircraft were stationed at RAF Sumburgh in the Shetland islands group from 4 November, and from here flew daily sorties to monitor weather conditions in the Tromsø area. On the same day, 39 Lancaster bombers (20 and 19 of Nos 9 and 617 Squadrons respectively) were despatched to airfields in northern Scotland in preparation for the operation. A gale warning was issued that night and the raid was cancelled as a result on the morning of 5 November. Both squadrons returned to their home bases during the day. The two squadrons deployed to Scotland once again on 7 November, but soon returned to their home bases when the attack was cancelled.

On 10 November, the Lancaster crews were briefed for another attempt on Tirpitz. Both squadrons moved to northern Scotland on 11 November after meteorological reports had suggested that there would be clear weather over Tromsø for up to two days. The aircraft were split between the RAF bases at Kinloss, Lossiemouth and Milltown.

Tirpitz's defensive capabilities had been improved after 'Obviate'. More Flak guns had by now been emplaced in the Tromsø area and anti-torpedo nets had been laid around the battleship. These changes enhanced the protection offered by the Flak ships Nymphe and Thetis and also by several shore-based Flak batteries. Dredging operations to reduce the depth of the water below the battleship’s hull began on 1 November, and by 12 November were half complete. The smoke generators that had previously helped to shield Tirpitz in the Kaafjord were still being installed at the time of 'Catechism' and were not yet operational. In their place, seven fishing boats fitted with smoke generators were positioned near the battleship, but these were not capable of generating a smokescreen that could completely cover Tirpitz.

The battleship’s crew continued regular training exercises, and remained concerned about further air attacks. On 4 November, Tirpitz's commanding officer, Kapitän Wolf Junge, departed and was replaced by the ship’s executive officer, Kapitän Robert Weber. The latter believed that within three weeks the days would be short enough to prevent further air attacks. On 12 November around 1,700 men were on board Tirpitz.

A force of 38 German fighters was transferred to Bardufoss airfield after 'Obviate' to strengthen the Tromsø region’s air defences. These aircraft were part of Major Heinrich Ehrler’s Jagdgeschwader 5. The unit had been evacuated from Kirkenes in the far north-eastern region of Norway as Soviet forces advanced toward the town, and was disorganised at the time of 'Catechism'. Most of the pilots at Bardufoss were inexperienced and poorly trained, and the unit had not been properly briefed on Tirpitz's presence in the area. Ehrler arrived at Bardufoss on 9 November en route to Alta, and decided to remain there until the morning of 12 November to oversee an emergency training programme for the fighter pilots.

The decision to launch 'Catechism' was made in the early hours of 12 November. A weather forecast generated during the afternoon of 11 November predicted that clouds might be encountered over northern Norway. One of the Mosquito meteorological aircraft flew over the area that evening and, after returning to Scotland shortly after 00.00 on the night of 11/12 November, its crew reported encountering patches of cloud. Nevertheless, the commander of No. 5 Group, Air Marshal the Hon. Ralph Cochrane, decided to attempt another attack in the hope that the bombers would meet clear weather over Tromsø.

A force of 32 Lancaster bombers was despatched: No. 617 Squadron contributed 18 oi these, and No. 9 Squadron 13. As with 'Paravane' and 'Obviate', the dedicated bombers were complemented by a single Lancaster, of the RAAF’s No. 463 Squadron, outfitted as a film aeroplane to collect material for use in propaganda films. Seven of No. 9 Squadron’s Lancaster bombers, including that of its commanding officer, Wing Commander James Bazin, were unable to participate as they could not be cleared in time of the snow and ice that had formed on them overnight. The aircraft of No. 617 Squadron took off between 02.59 and 03.25, and those of No. 9 Squadron between 03.00 and 03.35. The aircraft flown by No. 9 Squadron’s deputy commander, Squadron Leader Bill Williams, was among those able to take-off, and he assumed command of the squadron.

The Lancaster bombers flew individually over the Norwegian Sea and, as in 'Obviate', crossed the Norwegian coast between Mosjøen and Namsos, where a gap in German radar coverage had been identified, but several of the bombers flew too far to the north and came within range of German radar stations. The attack force rendezvoused over the Torneträsk lake. After making two orbits, No. 617 Squadron’s commanding officer, Wing Commander 'Willie' Tait, fired a flare gun from his aeroplane to signal the force to proceed to Tromsø. Two of No. 9 Squadron’s Lancaster bombers failed to reach the Torneträsk lake in time, and returned to base without attacking.

The attack force proceeded on a north-westerly heading toward Tromsø, and climbed to 14,000 ft (4265 m) to clear the mountains along the border between Sweden and Norway. They were guided by radio homing signals transmitted by a Norwegian Milorg (military resistance) agent stationed near the border between the two countries. By the time the bombers reached the Tromsø area, both squadrons had formed into loose formations. No. 617 Squadron led the attack, followed by No. 9 Squadron. The Lancaster bombers were grouped into gaggles of four to six aircraft flying at altitudes of between 14,000 ft and 15,000 (4265 and 4570 m). The No. 463 Squadron film aeroplane approached Tromsø at 6,000 ft (1830 m), and dropped to 2,000 ft (610 m) to evade Flak fire at the start of the attack.

The German forces in the Tromsø area failed to respond adequately to the multiple warnings of the approaching British bombers. Between 07.39 and 08.50, several observation posts in the area had reported sighting Lancaster bombers. As the first aircraft to be spotted were flying to the east, it was thought that they might be headed to the USSR. Tirpitz was not notified of the reports until 08.15, and few reports were passed to the JG 5 detachment at Bardufoss. Tirpitz's air raid siren was sounded at 08.51, and Weber informed the ship’s crew seven minutes later that an attack was possible.

At around 09.15, Tirpitz contacted Bardufoss to request that fighters be despatched to provide air cover. This was too late for any of the fighters to reach Tromsø before the bombers arrived above the battleship. It was only at 09.18 that the local Luftwaffe command ordered the fighters to be scrambled, and as a result of various delays, the fighters did not start to take-off from Bardufoss until about 09.32. Ehrler took off first, but the other pilots were delayed from doing so for several minutes as the runway was blocked by the arrival of another aeroplane. Ehrler proceeded to the Tromsø area by himself, but was unable to locate the British bombers before they attacked. It is not clear where the other fighters were sent. One post-attack report stated they were sent to the border with Sweden, another that they proceeded to the Kaafjord, and two pilots claimed to have reached Tromsø after Tirpitz had been destroyed.

The weather over Tromsø continued to be clear as the attack force arrived in the area. Tait spotted Tirpitz from 20 miles (32 km) away, and later recalled that she was 'lying squat and black among her torpedo nets like a spider in her web, silhouetted against the glittering blue and green waters of the fjord'.

Tirpitz fired the first shots of the battle at 09.38 as she started to engage the bombers with her 380-mm (15-in) main guns from a range of 13.5 miles (22 km), firing time-fused fragmentation shells designed for anti-aircraft barrage fire. Other anti-aircraft guns also fired on the Lancaster bombers as they approached, but did not disrupt them. No smokescreen was present as the British aircraft flew to the north-west in the direction of their bombing positions.

The attack started at 09.41. Tait’s aeroplane was the first to drop its Tallboy, which hit Tirpitz. No. 617 Squadron completed its attack at 09.44, by which time all of the unit’s aircraft had bombed. No. 9 Squadron’s aircraft began dropping their Tallboy bombs at 09.45. By this time the battleship was on fire and covered in smoke. The last bomb was released at 09.49.

Tirpitz was rapidly destroyed. She was struck by two Tallboy bombs which penetrated her armoured upper deck, which varied in thickness from 100 to 120 mm (3.9 to 4.7 in). One hit to the port of the 'Bruno' turret in the forward section of the ship, but did not detonate. The other was dropped by Tait’s aeroplane and struck the ship’s port side amidships near the tracks for the aircraft catapult, and exploded over the port boiler room. This explosion caused severe damage that resulted in extensive flooding, fires throughout the ship and a list of 15° to 20° to port. Several other bombs detonated in the water near Tirpitz, causing further damage to her hull and additional flooding. These explosions also created large craters below the ship, and blew away much of the gravel that had been dumped beneath her. Another Tallboy probably hit Tirpitz: one historian has stated that this bomb ricocheted off the side of the ship, while others have claimed that it probably penetrated the armoured deck near 'Cäsar' turret in the after part of the ship and started a fire near a powder or shell magazine. Almost all the hits and near misses were on the port side of Tirpitz, a fact which which destabilised the ship and led her list to increase rapidly. Many sailors manning Tirpitz's Flak guns were killed or wounded by the bombs, resulting in a significant reduction in the volume of fire directed at the bombers.

After the first bomb had impacted his ship, Weber ordered the crew to evacuate the armoured citadel and attempt to counter the flooding. Despite the list, Weber expected that Tirpitz would not sink as the water beneath her hull was too shallow. Counter-flooding proved impossible as the controls for the necessary systems had been abandoned, and the volume of water flooding into the ship was well beyond their ability to fight even if all systems had been operational. At 09.45 Weber ordered the evacuation of the lower decks, and by this time the list had reached between 30° and 40° degrees. At 09.50 the magazine for 'Cäsar' turret exploded, causing further extensive damage. Tirpitz's list increased rapidly, and the ship was soon lying on her side. Weber then gave the order to abandon ship. The battleship continued to heel over, and capsized at 09.52. Almost 1,000 of her crew had either been killed by this time, or were trapped inside the hull.

The crews of several Lancaster bombers observed Tirpitz capsize.The film aeroplane of No. 463 Squadron made a final pass over the battleship at an altitude of just 50 ft (15 m) to capture footage of the event. Just after 11.00, a photo-reconnaissance Mosquito overflew the Tromsø region, and photographed the wreck. The Secret Intelligence Service agent Egil Lindberg also sent radio reports from Tromsø confirming that Tirpitz had been destroyed.

The German forces in the Tromsø area made a major effort to rescue the surviving members of Tirpitz's crew. Within two hours, 596 had swum to shore or been rescued from the water. Others were trapped in air pockets within the wreck, and were doomed unless they were able to move to what was once the bottom of the ship, and be rescued before their air supply ran out. Shortly after Tirpitz capsized, parties of sailors climbed onto the hull and painted marks on locations where they heard signs of life. Oxyacetylene torches were needed to cut into the thick hull, and no such equipment was initially available: local Norwegian civilians who owned torches hid them, and only one could be found. A total of 87 men was rescued from within the hull in the 24 hours after the attack. Cutting continued for two further days, and was finally abandoned when it was assessed that the oxygen supply inside the wreck must have been exhausted; no survivors were recovered during this period. Estimates of the total number of sailors and officers killed vary, with the most common figures lying between 940 and 1,204. Weber and all of his senior officers were among the dead.

Many Norwegian civilians in Tromsø were happy that Tirpitz had been destroyed, not least as it meant the end of an order requiring that they billet members of her crew. Several civilians who showed pleasure at the event in public were arrested by the Gestapo. Other Norwegians were saddened by the way that the battleship’s crew had died.

Work on stripping Tirpitz's wreck began soon after rescue efforts had been terminated, and continued until the late 1950s. Before the end of the war, German personnel had removed the ship’s bronze propellers and some other components so they could be melted down. The wreck was sold to a Norwegian scrap dealing company in 1948, and was broken up in situ. Salvage work concluded in 1957, by which time most remnants of the battleship had been removed. The human remains which were recovered from the wreck by scrappers were initially buried alongside unwanted parts of Tirpitz, but this practice was ended after complaints by a local church minister. The remains of hundreds of others were recovered and buried in Norwegian cemeteries.

One of No. 9 Squadron’s Lancaster aircraft had been badly damaged by Flak fire, and its pilot decided to attempt a crash-landing in Sweden. The crew was able to make radio contact with Swedish military forces manning a small airfield at Naisjärv, who prepared it for the bomber. When one of the Lancaster’s engines failed as the aeroplane was attempting to land, the pilot made a belly landing in a field near a village. None of the crew was injured, and all were interned by the Swedish government: all of the men were subsequently repatriated to the UK.

The return flights of the other Lancaster bombers were complicated by adverse winds. Fuel shortages forced many of the aircraft to divert to alternate airfields, but all landed safely during the afternoon of 12 November. Two Lancaster bombers landed at RAF Banff: one of them was still carrying its Tallboy bomb, which had hung up, and after taxiing to a halt and the crew had left the aeroplane, the Tallboy came free and fell to the concrete. The film aeroplane flew directly to its home station at RAF Waddington, where its pilot was debriefed by Cochrane. The bomber squadrons returned to their home bases over the next two days.

Tirpitz's removal of the equation of naval strength in the northern part of the European theatre made it possible for the Allies to redeploy resources to other theatres. More than half of the Home Fleet was deployed elsewhere, including many ships sent to the Pacific to fight Japanese forces.

The loss of Tirpitz was a disaster for the German military forces in northern Norway. In addition to the heavy loss of life, the destruction of the battleship left the Kriegsmarine without any of the capital ships needed to threaten Allied convoy routes. Ehrler and several personnel assigned to observer posts, Flak batteries and ships were court-martialled and imprisoned. Ehrler was convicted in relation to leaving his unit’s operations room under the command of a non-commissioned officer on 12 November, sentenced to three years' imprisonment, but was released after a month and demoted. Dönitz ordered that an inquiry into why the battleship had capsized, and this concluded that 'the actual depth of the prepared berth did not conform with the requirements and directions of the commander-in-chief'.

It is unclear why the fighters at Bardufoss failed to protect the battleship. Much of the relevant documentation did not survive the war, and accounts from survivors are at times contradictory.

The British undertook several analyses of the attack. In December 1944, No. 5 Group’s headquarters investigated the accuracy of the bombing. This analysis found that No. 617 Squadron had been much more accurate than No. 9 Squadron, possibly as a result of the fact that the latter’s bomb-aimers had inputted an inaccurate wind speed into their sights. The superior Stabilized Automatic Bomb Sight fitted to No. 617 Squadron’s aircraft may have also contributed to the difference.