Monday, August 10, 2015

Radar Use: Bismarck and Prinz Eugen, 1827 May 1941

Portrait of Bismarck and Prinz Eugen during the Battle of the Denmark Strait by Michel Guyot. (Image courtesy of Michel Guyot) © Michel Guyot all rights reserved

Late in the evening of 18 May 1941 two new units of Raeder's surface fleet left their Baltic port after completing careful shakedown cruises and training. They were the 15 inch battleship Bismarck and her consort, the 8 inch heavy cruiser Prinz Eugen. The former was named for the chancellor whose foreign policies had made friendship with England a vital element, attained by avoiding naval and colonial rivalry. The latter was named for the comrade-in-arms of Winston Churchill's ancestor, John Churchill, 1st Duke of Marlborough, Eugen's partner in a long and successful struggle by the Germans and the British against Louis XIV's attempts to subjugate Europe. Both ships were the ultimate of naval architecture. Both were equipped with Seetakt; both had special radar rooms as a part of the original design. Their assignment was commerce raiding under the command of Admiral Lütjens. More was expected of them than of previous surface actions, for with their armor, speed and radar they would be difficult to stop, an opinion shared in Berlin and London.  

Previous surface raiding had found the Royal Navy radar poor and the raiders making good use of their own. Now the balance was to swing in the other direction with the Royal Navy, Coastal Command and the Fleet Air Arm radar equipped to some extent. The exact time and route of the pair were not known to the Admiralty, but the break-out was no surprise, and a significant reception was prepared.

On the 21st the two were sighted at Bergen by air reconnaissance. That observation had been followed up on the following day in near-impossible flying weather, and the harbor was found to be empty. The two had sailed for the Denmark Strait, at the time about two-thirds blocked by ice and with most of the remainder the recent depository of 6100 mines. Retreating ice had left a safe passage that Seetakt easily traced, allowing them to avoid the floating bergs as well as the pack ice even in the deep fog that kept British non-radar air patrols from sighting them.  

The cruiser Suffolk had received one of the first two 7.5 m type 79Zs in May 1939, later upgraded to type 279, and now was also equipped with the 50 cm type 284 radar for directing the fire of her main armament. She waited at her station at the exit of the mine field. The cruiser Norfolk, which patrolled 80 km to the west, had only the 1.5 m fixed-antenna type 286M, the one that required swinging ship for direction.  

At 1920 hours on the 23rd the Suffolk and the Bismarck sighted one another visually as the latter broke briefly from a fog bank. The type 284 transmitter tubes were pushed to the limit to gain the needed power at such short wavelength; this normally allowed operation for only a couple of hours at a time, not too restrictive for gun-laying but hardly suitable for searching. The vertical lobe structure of the 7.5 m set precluded using it for surface search except at very close range. It was the intermittent use required to conserve the 284 that caused the British sighting to be visual. Suffolk scurried for fog before 15 inch shells could be sent her way, got off a sighting report and began tracking the big ship with the 50 cm type 284.  

The Bismarck, whose two 80 cm sets were not restricted in duration of operation, had located the Suffolk both with radar and underwater sound before the visual sighting. Fortunately for the cruiser the Seetakt did not incorporate lobe switching and thus could not direct blind fire, having a directional accuracy of only 5°. Because of iced insulators on the radio antenna the Suffolk's first sighting report was received only by the Norfolk and the Prinz Eugen, where it was promptly decoded. The Norfolk soon had a glimpse of the battleship and narrowly escaped a salvo of heavy shells. The shock of gunfire had the effect of knocking out the forward Seetakt to Lütjens's great displeasure, so Prinz Eugen had to lead, as both her radars still functioned. The Suffolk managed to keep her quarry in optical or radar sight and hold the Norfolk close with radio. The Admiralty soon learned of the chase and dispatched the new battleship Prince of Wales and the flagship Hood to intercept. They met the enemy early in the morning of the 24th, despite the Suffolk having lost contact a few hours before. Vice Admiral L E Holland, commanding the squadron, ordered complete radio silence for his ships, including radar, until the German ships were sighted, his fear being that with their greater speed the Germans could escape if alerted.  

The Hood was the finest of that most unfortunate kind of warship, the battle cruiser. As large as a battleship with guns as heavy, it sacrificed armor to gain speed. It was a stylish idea in naval circles before the demonstration that a 5 knot difference in speed did not matter to well-aimed projectiles that easily penetrated thin steel. Three ships of this type had disappeared in the Battle of Jutland in catastrophic explosions. (The German battle cruisers Scharnhorst and Gneisenau traded gun power for speed rather than armor plate, having only 11 inch artillery, small for battleship-class vessels.) 
The Hood had a type 279M air warning radar and a type 284 gun-laying set, but radar did not protect her from the first salvos of the two German ships, and she blew up in a mighty explosion, the presumed consequence of a heavy shell penetrating her thin deck armor and detonating the magazines. The German optical fire control was up to the same high standards it had so startlingly demonstrated in action in the North Sea in the previous war and the Bismarck's defective radar was not missed.  

The Prince of Wales had a 3.5 m type 281 air warning set and nine fire control radars, but the ship was so new that civilian workmen were still on board, as bad luck would have it, because of problems with the main armament. She was also so new that the gunnery officers had not incorporated radar into their procedures. The radar officer reported accurate ranges throughout the brief fight, but they were not used in calculating gun orders, and it was only the sixth salvo that had the correct range. So it came to pass that in the first encounter of big-gun ships equipped with radar the use of the new technique is enveloped in fog: the forward German set on which the First Gunnery Officer would have relied was dead, and the British set was ignored. What the Hood did will remain unknown, but her first salvo was not on target.  

The Prince of Wales developed serious malfunctions in her artillery and sustained enough damage to cause her to withdraw behind a smoke screen. The Bismarck had unintentionally begun replacing fuel oil with seawater though retaining a speed of 28 knots. Why Lütjens did not pursue and very likely sink the Prince of Wales is a puzzle few have understood. At this point the Bismarck was sufficiently damaged that commerce raiding without repair was not possible, and sinking the two most powerful ships of the Royal Navy would have certainly justified the attempt. Lütjens detached the Prinz Eugen to proceed independently to the south and began a straight run for the safety in the Bay of Biscay. 
Now the Bismarck was pursued by an ever growing assortment of very heavy ships with the Suffolk again doggedly tracking, but on the 25th she lost radar contact, the almost certain consequence of the intermittent use required of the 284. Lütjens was so impressed with the ability of the Suffolk to follow that he broke radio silence to inform his chief of the radar capability of which he had not been informed and the range capability of which he greatly overestimated. The overestimation probably resulted from navigational errors of one or both ships, as Lütjens compared his calculated position with the continual flow of messages that the Suffolk was transmitting. Lütjens's message allowed British radio-direction finders to get a rough idea of his position, but at the time he incorrectly thought he was being held fast by British radar.  

This incident is linked to reports that the Bismarck had a passive radar receiver and had monitored the tracking. If so, it must have been an experimental set of which there is no other record [14], and the passive receivers that first came into use more than a year later would not have responded to 50 cm waves. It is plausible that the radar operators, presumably briefed on British use of long waves, picked up on communications receivers some of the abundant 7.5 m transmissions, which they would have recognized as radar. Given the circumstances it is unlikely that they would have realized that this equipment was incapable of observing them at the ranges involved.  

A sighting through the swirling clouds over a rough sea by a Catalina flying boat equipped with ASV mark II established the Bismarck's position accurately enough for the cruiser Sheffield to be ordered to pick her up with the type 79Y radar, if possible. At this point aircraft from the carriers Victorious and Ark Royal were decisive. Both were equipped with the famous Swordfish biplanes, slow but very tough and possessed of a remarkably long range and a deceiving agility, if not encumbered with torpedo or bomb. They probably sank more tonnage than any other torpedo bomber during the war and were valuable participants until the very end. We shall return to them when describing action in the Mediterranean, the high point of the Swordfish's service.  

One of the Swordfish from each carrier was equipped with ASV mark II, and green fliers from the Victorious, which had not had time to work up her crews, even to allow them to practice take-off and landing from the deck, found the target and got an ineffective hit on the armor belt. The first attack by 14 planes from the much more experienced Ark Royal went after the shadowing Sheffield instead, of whose presence they had not been informed, but their torpedoes missed. Their next attack of 15 planes found the Bismarck with radar in conditions of 'low rain cloud, strong wind, stormy seas, fading daylight and intense and accurate enemy gunfire'. One torpedo struck the armor belt, another jammed the steering gear, and with that the great ship was doomed. The radar that found the target also found the home ship, and all 15 aircraft returned, to be sure with wounded crewmen, perforated fabric and three crash landings.  

With the stricken ship no longer able to reach the protective cover of land-based bombers, dawn came as a death sentence to be executed by the battleships Rodney ordered to the spot with a deck cargo for installation in America and 300 passengers and the King George V. Accurate fire, soon delivered at close range, destroyed the ship that refused to surrender. There are several accounts of this famous battle. The reader is advised to read the one by the Bismarck's Adjutant and Fourth Gunnery Officer and that of the under-water explorer who found the wreck in 1989.  

 The sinking of the Bismarck put an end to German surface raiding with large ships. Even without that dramatic climax it was becoming increasingly obvious that it simply did not pay. The Scharnhorst cost as much to build as 100 submarines, required a huge crew and elaborate supply, and was not immune to sinking. There was an attempt by the pocket battleship Lützow to renew raiding, but her sortie of 10 June 1941 was countered by a torpedo-plane attack that sent her back to Kiel for months of repair. When Hitler attacked the Soviet Union, he required many of his surface units for the Baltic. The disguised raiders continued until the Royal Navy removed them, their tankers and supply ships from the seas. Commerce raiding would be left to the U-boats of Konteradmiral Karl Dönitz, and all traces of romance disappeared.  

The use by the Kriegsmarine in 1939-1941 of Seetakt was a most impressive consequence of the power of pure radar, the result of a naked radar set mounted on a ship for which no thought had been given as to what its exact tactical function was to be. The naval personnel received little training, but the set was simply ideal for a commerce raider. It was the kind of thing that every alert officer recognized when he first encountered it the torpedo officer of the Hipper a conspicuous exception. Application came immediately and instinctively. There is no evidence of captains considering radar as just 'an interesting device'; they regarded its malfunction to be a major problem for which they demanded the delivery of spare parts by special ship and submarine.  

It had not been planned that way by Raeder. On first seeing a radar demonstration he was impressed enough not to interfere but cautioned Kühnhold that his primary research mission was under-water sound. It was the line officers who recognized the new weapon for its value, and their use of it in the few months of surface action was beyond criticism. Except for a technically dull-witted command they could have had blind-fire directed gunnery in 1938. German naval radar had a brilliant beginning that led nowhere.  

Typical of the want of understanding at the top was the vacancy of the position of Chef der Abteilung Entwicklung der Nachrichtenmittel (Chief for Development of Signals) from November 1939 until April 1943! Moreover it was not until mid-1941 that the Marine-Nachrichtendienst (Navy Signals Service) was formed and with it a naval career specialty for radar, Seetaktischer Funkmessdienst (Tactical Radar Service). Progress remained slow, and Dönitz was to find his U-boats completely outclassed in either defensive or offensive radar techniques.  

A comparison between the two navies offers instruction about their respective use of radar 21 months into the war. The Germans had mounted a prototype Seetakt in 1938, modified it in small ways, and haltingly made it reliable aboard a warship, the obvious responses of competent engineers; it was their only shipborne radar for months yet to come. Despite the Navy's introduction of the equally good air-warning Freya, it was never taken to sea except on vessels in the North Sea as part of the country's air warning system, nor was the excellent gun-laying Würzburg used aboard ship to improve AA fire, although GEMA soon adapted the Seetakt for dual purpose. The British by contrast had by May 1941 almost a dozen different kinds of shipborne radar installed, but it was not until the 10 cm type 271 appeared, with sea trials in March and April 1941, that they had a surface-search set competitive with Seetakt. In their hunt for the Bismarck only one shipborne radar set of the entire pack of hounds was effective, and its inability to maintain continuous search caused it to lose the target vessel at a critical moment, saved by the splendid ASV mark II. It remains a puzzle that a naval command that gave high priority to radar placed so little importance on surface search equipment. The answer to the puzzle probably lies in Britain's approach to radar from the long-wave side.

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