HMS Graph (P715) - AbsoluteAstronomy.com

Pennant number

In the modern Royal Navy, and other navies of Europe and the Commonwealth, ships are identified by pennant numbers...

P715) was a German Type VIIC U-boat

U-boat

U-boat is the anglicized version of the German word U-Boot , itself an abbreviation of Unterseeboot , and refers to military submarines operated by Germany, particularly in World War I and World War II...

used by the British Royal Navy

Royal Navy

The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

during World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

.
Commissioned as the U-570 in the German

Nazi Germany

Nazi Germany , also known as the Third Reich , but officially called German Reich from 1933 to 1943 and Greater German Reich from 26 June 1943 onward, is the name commonly used to refer to the state of Germany from 1933 to 1945, when it was a totalitarian dictatorship ruled by...

Kriegsmarine

The Kriegsmarine was the name of the German Navy during the Nazi regime . It superseded the Kaiserliche Marine of World War I and the post-war Reichsmarine. The Kriegsmarine was one of three official branches of the Wehrmacht, the unified armed forces of Nazi Germany.The Kriegsmarine grew rapidly...

in mid-1941, she was attacked and captured on her first patrol.

As well as providing information on German submarines, she was used on active service from 1942 to 1944 when she was withdrawn due to problems maintaining her. She ran aground off the west coast of Scotland en route to the breakers and was largely scrapped there. She was the only German U-boat to be taken into Allied service and to see active service with both sides during the war.

Design and construction

The submarine was built to the German Type VIIC design. She had a displacement

Displacement (ship)

A ship's displacement is its weight at any given time, generally expressed in metric tons or long tons. The term is often used to mean the ship's weight when it is loaded to its maximum capacity. A number of synonymous terms exist for this maximum weight, such as loaded displacement, full load...

of 769 tonnes (757 LT) when surfaced, and 871 t (857 LT) when submerged. The boat was 67.1 metre long, with a beam of 6.2 metre, and a draught of 4.74 metre. The diesel-electric propulsion system provided a maximum speed of 18.8 knots (10.2 m/s) surfaced or 7.6 knots (4.1 m/s) submerged. The U-570 had a fuel capacity of 109 long tons (110.7 MT) which gave a range of 7500 nautical miles (13,890 km) at 10 knots (5.4 m/s). The test depth of the submarine was 230 metres (754.6 ft).

The main armament consisted of five 21 inches (533 mm) torpedo tubes; four in the bow, and the fifth in the stern. A total of 14 torpedos could be carried – five in the torpedo tubes, seven reloads inside the pressure hull and a further two outside the pressure hull. The boat was fitted with a C35 88 mm/L45 deck gun

Deck gun

A deck gun is a type of artillery cannon mounted on the deck of a ship or submarine.The deck gun was used as a defensive weapon against smaller boats or ships and in certain cases where torpedo use was limited. Typically a crew of three; gunner, loader, and layer, operated the gun, while others...

(with around 150 rounds of ammunition) and a 2cm Flak 30 anti-aircraft gun. A 28cm Stereoscopic rangefinder was carried for use with the anti-aircraft gun, and a number of machine guns were also carried.

U-570 was laid down by Blohm & Voss at Hamburg

Hamburg

-History:The first historic name for the city was, according to Claudius Ptolemy's reports, Treva.But the city takes its modern name, Hamburg, from the first permanent building on the site, a castle whose construction was ordered by the Emperor Charlemagne in AD 808...

on 21 May 1940. The submarine was launched on 20 March 1941.

Kriegsmarine service

The U-570 was commissioned into the Kriegsmarine on the 15 May 1941. After a series of short testing and commissioning trips in the Baltic, she moved to Norway where she carried out short training voyages and fired practice torpedoes. By 25 July, she had moved to the German U-boat base at Lofjord

German U-boat bases in occupied Norway

German U-boat bases in occupied Norway existed between 1940 and 1945, when the German Navy, the Kriegsmarine, converted several naval bases in Norway into Submarine bases. Norwegian coastal cities became available to the German Navy after the invasion of Denmark and Norway in April 1940...

, part of Trondheimsfjord

Trondheimsfjord

The Trondheimsfjord , an inlet of the Norwegian Sea, is Norway's third longest fjord at long. It is located in the west central part of the country, and it stretches from Ørland in west to Steinkjer in north, passing the city of Trondheim on its way...

, around 13 kilometres (8 mi) north of Trondheim.

In late-August 1941, B-Dienst

B-Dienst

The B-Dienst was a German naval codebreaking organisation. During World War II, B-Dienst solved British Naval Cypher No. 3, providing intelligence for the Battle of the Atlantic, until the British Admiralty introduced Naval Cypher No. 5 on 10 June 1943. B-Dienst also solved a number of merchant...

(the German naval codebreaking organisation) became aware of a large concentration of Allied merchant ships in the region of the North Atlantic south of Iceland. Admiral Karl Dönitz

Karl Dönitz

Karl Dönitz was a German naval commander during World War II. He started his career in the German Navy during World War I. In 1918, while he was in command of , the submarine was sunk by British forces and Dönitz was taken prisoner...

ordered sixteen U-boats to the area. The U-570 was to be one of these and, on the morning of 24 August, she put to sea on her first war patrol. Her planned mission was to patrol the area south of Iceland before proceeding to the U-boat base at La Pallice, France. She carried provisions for four weeks at sea.

The submarine was commanded by Kapitänleutnant Hans-Joachim Rahmlow. He was an experienced naval officer, but had only recently transferred to U-boats, having previously been a gunnery and coastal defences specialist. He had commanded the training submarine , but had carried out no war patrols. Likewise, the First Watch Officer (second-in-command) had only served a few months with the U-boat branch, after serving on destroyers and the Second Watch Officer had little experience, having only recently been commissioned. The engineer was the only officer (and one of only four on-board) who had served on a U-boat war patrol. While the boat's petty officers had several years of navy service, many of the enlisted crew were still new to the German navy and had only a few months of U-boat training.

The U-570s inexperienced crew was not unusual for the time. British interrogation of rescued crew-members of the —sunk on her first patrol in September 1941—revealed that only seven out of 48 had previously seen a war patrol.

Capture

On 27 August, U-570 spent much of the morning submerged. She had been four days at sea and this was to give respite to a crew that was suffering acutely from seasickness (several had been incapacitated). She surfaced at position 62°15′N 18°35′W at around 10:50 am, and was immediately detected by the radar of a nearby RAF Lockheed Hudson

Lockheed Hudson

The Lockheed Hudson was an American-built light bomber and coastal reconnaissance aircraft built initially for the Royal Air Force shortly before the outbreak of the Second World War and primarily operated by the RAF thereafter...

bomber of 269 Squadron

No. 269 Squadron RAF

No. 269 Squadron RAF was a maritime patrol unit of the Royal Air Force that saw service in World War I, World War II, and the Cold War.-World War I:...

operating from Kaldaðarnes

Kaldadarnes, Iceland

Kaldaðarnes is an ancient farm estate in Iceland on the banks of Olfus river, around 8 km west of Selfoss. Records of a farm at this location exist back to year 1200 where it is stated that Kaldadarnes was one of few farms with rights to offer ferry service across the Olfus river.At...

, Iceland.

Rahmlow, who had climbed out onto the bridge, heard the approaching Hudson's engines and ordered a crash-dive. However, the aircraft reached the submarine before she was fully submerged and dropped four 250 pounds (113.4 kg) depth charges—one detonated just 10 yards (9.1 m) from the boat.

The U-boat quickly resurfaced and around ten of the crew emerged. The Hudson opened fire on them with machine guns, but ceased when the U-boat crew displayed a white sheet

White flag

White flags have had different meanings throughout history and depending on the locale.-Flag of temporary truce in order to parley :...

. An account of what happened was subsequently given to British naval intelligence interrogators by the captured crew members—the depth charge explosions had almost rolled the boat over, knocked out all electrical power, smashed instruments, caused water leaks and contaminated the air on the boat. The inexperienced crew believed the contamination to be chlorine

Chlorine

Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...

, caused by acid from leaking battery cells mixing with sea-water, and the engine-compartment crew panicked and fled forward to escape the gas. Restoring electrical power—for the underwater electric motors and for lighting—would have been straightforward, yet there was nobody remaining in the engine compartment to do this. The submarine was dead in the water and in darkness. Rahmlow believed the chlorine would make it fatal to stay submerged so he resurfaced. The sea was too rough for the crew to man their anti-aircraft gun so they displayed a white flag to forestall another, probably fatal, depth charge attack from the Hudson—they were unaware the aircraft had dropped all its depth-charges.

Most of the crew remained on the deck of the submarine as the Hudson circled above them. A radio request for help saw it being joined by another Hudson and a Consolidated Catalina flying boat of 209 Squadron

No. 209 Squadron RAF

No. 209 Squadron of the British Royal Air Force was originally formed from a nucleus of "Naval Eight" on 1 February 1917 at Saint-Pol-sur-Mer, France, as No. 9 Squadron Royal Naval Air Service and saw active service in both World Wars, the Korean War and in Malaya...

, with a full load of depth-charges. The German crew radioed their situation to the German naval high-command, destroyed their radio, smashed their Enigma machine

Enigma machine

An Enigma machine is any of a family of related electro-mechanical rotor cipher machines used for the encryption and decryption of secret messages. Enigma was invented by German engineer Arthur Scherbius at the end of World War I...

and dumped its parts overboard along with the boat's secret papers. Admiral Dönitz later noted in his war diary that he ordered U-boats in the area to go to U-570s assistance after receiving this report and the responded, but was prevented from reaching the U-570 by Allied air patrols.
The U-570s transmission was in plain language and it was intercepted by the British. Admiral Percy Noble, commander of Western Approaches Command

Western Approaches Command

Commander-in-Chief, Western Approaches was the commander of a major operational command of the Royal Navy during World War II. The admiral commanding, and his forces, sometimes informally known as 'Western Approaches Command,' were responsible for the safety of British shipping in the Western...

, immediately ordered a small armada of ships to race to the scene. By early afternoon, fuel levels had forced the Hudsons to return to their base in Iceland. The Catalina, a very long-range aircraft, was ordered to watch the submarine until Allied ships arrived. If none came before sunset, the aircraft was to warn the U-570s crew to take to the water, then sink her. The arrival of the first vessel—the anti-submarine trawler

Naval trawler

A naval trawler is a vessel built along the lines of a fishing trawler but fitted out for naval purposes. Naval trawlers were widely used during the First and Second world wars. Fishing trawlers were particularly suited for many naval requirements because they were robust boats designed to work...

HMT Northern Chief—averted this. The Catalina returned to Iceland after flying in circles over the U-boat for 13 hours.

The German crew remained on board U-570 overnight; they made no attempt to scuttle their boat as Northern Chief had signaled she would open fire and not rescue survivors from the water if they did this. During the night, four more naval trawlers and the destroyers and reached the scene. At daybreak, there was a series of signal lamp

Signal lamp

A signal lamp is a visual signaling device for optical communication . Modern signal lamps are a focused lamp which can produce a pulse of light...

messages between the Allies and Germans, with the Germans repeatedly requesting to be taken off as they were unable to stay afloat, and the British refusing to evacuate them until they secured the submarine and stopped it from sinking—the British were concerned that the Germans would deliberately leave behind them a sinking U-boat if they were evacuated. The situation became more confused when a small float-plane (a Northrop N-3PB

Northrop N-3PB

The Northrop N-3PB Nomad was a single-engined American floatplane of the 1940s. Northrop developed the N-3PB as an export model based on the earlier Northrop A-17 design. A total of 24 were purchased by Norway, but were not delivered until after the Fall of Norway during the Second World War...

of 330 (Norwegian) Squadron) appeared. Unaware of the surrender, it attacked the U-570 with small bombs and fired on the Northern Chief (which returned fire). No damage was done and Burwell ordered the aircraft away by radio.

The weather worsened; several attempts to attach a tow-line to the U-boat were unsuccessful. Believing the Germans were being obstructive, Burwell's captain, S.R.J. Woods ordered warning shots to be fired with a machine gun, but five of the German crew were accidentally hit and slightly wounded. With much difficulty, four British sailors from the trawler HMS Kingston Agathe reached the submarine using a Carley float

Carley float

The Carley float was a form of invertible liferaft designed by American inventor Horace Carley . Supplied mainly to warships, it saw widespread use in a number of navies during peacetime and both World Wars until superseded by more modern rigid or inflatable designs...

(a liferaft). After a quick search failed to find the U-boat's Enigma machine, they attached a tow line and carried out the transfer of the five wounded men and the submarine's officers to the Kingson Agathe. The remaining crew were taken on board HMCS Niagara, which by this time had come alongside the U-boat.

The ships began slowly sailing to Iceland with the U-570 under tow, and with a relay of Hudsons and Catalinas constantly patrolling overhead. They arriving at dawn on 29 August at Þorlákshöfn

Þorlákshöfn

Þorlákshöfn is a town on the southern coast of Iceland in the Municipality called Ölfus.The town name is named after Þorláki Helga who was bishop at Skálholt...

. There, the submarine was beached as she had been taking on water and was thought to be in danger of sinking.

Salvage and Repair

Two days after the submarine's arrival, a British submarine commander—Lieutenant George Colvin—together with a team of engineering warrant officers and civilian technical experts arrived at Þorlákshöfn from Britain to carry out the U-570s initial examination and salvage.
Colvin's team was able to restore lighting and buoyancy; U-570 was re-floated and towed around the coast to the British naval base at Hvalfjörður

Hvalfjörður

Hvalfjörður is situated in the west of Iceland between Mosfellsbær and Akranes. The fjord is approximately 30 km long and 5 km wide....

where repairs were made that would enable her to make the trip to Britain under her own power.

The British discovered that the depth charge damage to the U-boat was not critical—there were leaks in some of the ballast tanks and a small leak in a fuel tank. Around one third of the battery cells were cracked and the bow had been buckled. Water had leaked in through a valve that had been unseated by the explosions and through glass gauges that had broken; other damage was minor and no evidence of chlorine gas found. In his report, Colvin stated his opinion that there was no evidence of any damage control

Damage control

Damage control is a term used in the Merchant Marine, maritime industry and navies for the emergency control of situations that may hazard the sinking of a ship...

being carried out and that an experienced submarine crew would have been easily able to improvise repairs, stay submerged and likely evade the air-attack. After their surrender, the German crew had attempted to destroy instruments and fittings, but, with the exception of the wrecked radio and the damaged torpedo firing computer, the attempt appeared half-hearted and the damage was not significant. Also, useful papers had missed destruction. Copies of encrypted signals and their corresponding, plain-language, German texts were found—material of use to the British Enigma code breaking

Cryptanalysis of the Enigma

Cryptanalysis of the Enigma enabled the western Allies in World War II to read substantial amounts of secret Morse-coded radio communications of the Axis powers that had been enciphered using Enigma machines. This yielded military intelligence which, along with that from other decrypted Axis radio...

effort. A significant discovery was the U-boat commander's handbook, which provided context and background information for the decrypted signals. The British, unfamiliar with German naval procedures, abbreviations and jargon, sometimes found German naval traffic hard to understand even when decrypted.

U-570 spent three weeks at Hvalfjörður, being repaired and taking short sea trials to test the engines and steering. On 23 September, she was carefully inspected by US Navy officers who had been dispatched to Iceland for that purpose; one of the submarine's G7a torpedo

G7a torpedo

The G7a or G7a/T1 was the standard issue Kriegsmarine torpedo during the early years of World War II.- Design :The torpedo was 53.3cm in diameter, 7.163 m in length, and with a warhead of 280 kg of Hexanite, and was standard issue for all U-boats of the war.The torpedo was of a straight-running...

es was removed and handed over to the Americans. An eye-witness recalls that at one point, a Hudson bomber flew low over U-570, signalling with a Morse lamp, "This ****** is mine."
On 29 September, the submarine set out for the UK, manned by a Royal Navy prize crew

Prize crew

Prize crew is a term used to indicate a number of crew members of a ship chosen to take over the operations of a captured ship.In the early days of sailing and up into the American Civil War, capturing enemy ships was quite common...

under the command of Lieutenant Colvin. Escorted by the destroyer HMS Saladin

S class destroyer (1916)

The S class were a class of 67 destroyers built from 1917 for the Royal Navy. The design was based on the Admiralty modified R class and all ships had names beginning with S or T....

and the trawler HMS Kingston Agathe - she sailed on the surface as her diving planes had been damaged by the beaching at Þorlákshöfn. Her arrival at Barrow-in-Furness

Barrow-in-Furness

Barrow-in-Furness is an industrial town and seaport which forms about half the territory of the wider Borough of Barrow-in-Furness in the county of Cumbria, England. It lies north of Liverpool, northwest of Manchester and southwest from the county town of Carlisle...

on 3 October was filmed by Pathé News

Pathe News

Pathé Newsreels were produced from 1910 until the 1970s, when production of newsreels was in general stopped. Pathé News today is known as British Pathé and its archive of over 90,000 reels is fully digitised and online.-History:...

newsreel cameras, and reported in the press. The capture would later be featured in British propaganda. The capture of several other U-boats, such as the (which had sunk whilst under tow) was kept secret to conceal the seizure of their code-books and Enigma machine

Enigma machine

s. U-570s situation had been reported to the German high command. Also, so many ships, aircraft and personnel had been involved in her capture that any attempt at secrecy would have been futile.

She was placed in a dry-dock in the Vickers shipyard in Barrow. Her repair was complicated by depth-charge damage to her bow—her plating had been buckled, trapping four electrically powered G7e torpedo

G7e torpedo

The G7e or more appropriately the G7e/T2, G7e/T3, and G7e/T4 Falke torpedoes were, with the exception of the T4 model, the standard torpedoes for Germany during World War II...

es in their torpedo tubes. Two officers from the Royal Navy's Department of Torpedoes and Mines Investigations had the task of retrieving them for examination. The dock was evacuated while a volunteer shipyard worker cut the armed torpedoes free with an oxyacetylene cutter

Oxy-fuel welding and cutting

Oxy-fuel welding and oxy-fuel cutting are processes that use fuel gases and oxygen to weld and cut metals, respectively. French engineers Edmond Fouché and Charles Picard became the first to develop oxygen-acetylene welding in 1903...

under the officers' supervision. One of the officers—Lt Martin Johnson—then removed the Magnetic pistol

Magnetic pistol

Magnetic pistol is the term for the device on a torpedo or naval mine that detects its target by its magnetic field, and triggers the fuse for detonation...

s (detonators) from the torpedoes and made them safe—a dangerous task as the pistols were sensitive mechanisms and quite large enough to produce a lethal explosion. For this act, he was awarded the George Medal

George Medal

The George Medal is the second level civil decoration of the United Kingdom and Commonwealth.The GM was instituted on 24 September 1940 by King George VI. At this time, during the height of The Blitz, there was a strong desire to reward the many acts of civilian courage...

on 8 December 1942.

One of the Kriegsmarine flags of the U-570 was presented to the Hudson bomber pilot—Squadron Leader

Squadron Leader

Squadron Leader is a commissioned rank in the Royal Air Force and the air forces of many countries which have historical British influence. It is also sometimes used as the English translation of an equivalent rank in countries which have a non-English air force-specific rank structure. In these...

James Thompson—and is now part of the collection of the RAF Museum

RAF Museum

The Royal Air Force Museum London, commonly known as the RAF Museum, is a museum located on the former Hendon Aerodrome, dedicated to the history of aviation and the British Royal Air Force. The museum is a non-departmental public body sponsored by the Ministry of Defence and a registered charity...

(another flag is claimed to have come into the possession of a young, apprentice fitter at the Vickers Barrow shipyard). Thompson and his navigator/bomb-aimer—Flying Officer

Flying Officer

Flying officer is a junior commissioned rank in the Royal Air Force and the air forces of many countries which have historical British influence...

John Coleman—were also awarded the Distinguished Flying Cross

Distinguished Flying Cross (United Kingdom)

The Distinguished Flying Cross is a military decoration awarded to personnel of the United Kingdom's Royal Air Force and other services, and formerly to officers of other Commonwealth countries, for "an act or acts of valour, courage or devotion to duty whilst flying in active operations against...

on 23 September 1941. The captain of the Kingston Agate, Henry L’Estrange, was awarded the Distinguished Service Cross

Distinguished Service Cross (United Kingdom)

The Distinguished Service Cross is the third level military decoration awarded to officers, and other ranks, of the British Armed Forces, Royal Fleet Auxiliary and British Merchant Navy and formerly also to officers of other Commonwealth countries.The DSC, which may be awarded posthumously, is...

for his part in the capture.

German response

Initially, all the German naval high command knew of U-570s situation was her radio message, saying she was under air-attack and unable to submerge; they only learned of her capture from later British press reports. They were concerned for the security of their communications and Vice Admiral Eric Maertens, head of navy communications, was ordered to report on this. He concluded that in the worst case scenario—that is, the British had secured U-570s codebooks and Rahmlow had revealed to them his secret keyword—communications would be compromised until a new list of Enigma machine settings came into force in November. However, he believed this worst case to be unlikely and that the U-570s crew would have almost certainly destroyed their secret material. Even if they had not, the additional security of the commander's memorised, secret keyword would defeat British cryptanalysis.

In fact, the British code-breakers at Bletchley Park

Bletchley Park

Bletchley Park is an estate located in the town of Bletchley, in Buckinghamshire, England, which currently houses the National Museum of Computing...

found the extra security of the keyword procedure to be simply of "nuisance value". The U-570s crew had indeed destroyed their Enigma machine and code-books but the Germans were unaware of the Royal Navy's earlier capture of the 's secret material, thanks to which, the British had been breaking German naval cyphers since June 1941. British code-breaking would not be seriously impeded until February 1942, when a new naval Enigma cypher would remain unbroken for ten months—the so-called "Shark Blackout".

Months later, the German command was still trying to discover the fate of the U-570s codebooks. A system of coded messages, hidden in the text of apparently ordinary, personal letters, was used to order the captured U-boat ace Otto Kretschmer

Otto Kretschmer

Flotilla Admiral Otto Kretschmer was a German U-boat commander in the Second World War and later an admiral in the Bundesmarine. From September 1939 until being captured in March 1941, he sank 47 ships, a total of 274,333 tons. For this he received the Knight's Cross of the Iron Cross with Oak...

to report on this. However, they were unaware that this channel of communication with German prisoners had been discovered by the Allies.

Apart from Rahmlow, the U-570's officers were taken to an officers' prisoner–of–war camp at Grizedale Hall

Grizedale

Grizedale is a hamlet in the Lake District of England, in the middle of the Grizedale Forest, located north of Satterthwaite and south of Hawkshead...

in Cumbria

Cumbria

Cumbria , is a non-metropolitan county in North West England. The county and Cumbria County Council, its local authority, came into existence in 1974 after the passage of the Local Government Act 1972. Cumbria's largest settlement and county town is Carlisle. It consists of six districts, and in...

. This was nicknamed the U-boat Hotel by the British as, during the early part of the war, the majority of prisoners were naval officers rescued from sunken U-boats. There, Rahmlow (in absentia) and the U-570's other officers were tried by a "Court of Honour

Court of Honor

A court of honor is a semi-official or unofficial tribunal constituted to determine various questions of social protocol, breaches of etiquette, and other allegations of breaches of honor, or entitlement to various honors...

" convened by other German prisoners, including Otto Kretschmer. Rahmlow and his second-in-command, Berhnard Berndt, were found "guilty of cowardice"; the other two officers were "acquitted". On the night of 18/19 October, Berndt escaped from the camp. However, he was soon apprehended by a detachment of Home Guard and was shot when he tried to escape.

According to some sources, he had escaped from the camp with the stated intention of redeeming himself by making his way to the U-570s dockyard at Barrow–a distance of only 22 miles (35.4 km)–and somehow destroying her. Another source states he was forced to make an escape attempt by a group of senior German prisoners, who enforced a brutal regime of punishing those who held anti-Nazi views or who co-operated with the British, and that Berndt only broke away and ran from the Home Guard when he realized they were returning him to Grizedale Hall; they shot him dead after he ignored warning shots. The British placed Rahmlow in a camp with German Army and Air Force prisoners to avoid further incidents of this kind.

Royal Navy service

The disposition of the boat was initially uncertain. Winston Churchill

Winston Churchill

Sir Winston Leonard Spencer-Churchill, was a predominantly Conservative British politician and statesman known for his leadership of the United Kingdom during the Second World War. He is widely regarded as one of the greatest wartime leaders of the century and served as Prime Minister twice...

was favour of handing her over to the Americans for repair, both for propaganda and as a means of deepening then-neutral America's engagement in the Battle of the Atlantic. The Americans were eager to have her, but the Royal Navy objected. She was commissioned into the Royal Navy as HMS Graph on 19 September 1941, and assigned the Royal Navy pennant number N46. She was given a name beginning with a 'G' to signify German, i.e., denoting that Graph was a captured vessel. The name Graph was also chosen owing to the extensive testing carried out on her (and therefore the many "Graphs" drawn up), but was also a play on the German

German language

German is a West Germanic language, related to and classified alongside English and Dutch. With an estimated 90 – 98 million native speakers, German is one of the world's major languages and is the most widely-spoken first language in the European Union....

word Graf meaning "Count".

Trials

Once seaworthy, meticulous trials were conducted to measure every aspect of Graph's sailing and diving characteristics. Her safe diving depth was discovered to be 230 metres (754.6 ft)—much deeper than the British thought for this kind of boat. At the time, Royal Navy depth charges had a maximum depth setting of 170 metres (557.7 ft) so the Germans could dive out of their reach. Depth charges were soon modified to take account of this. The boat's acoustic and magnetic characteristics were examined by different Admiralty research establishments. Models, based on her, were used in experiments with underwater explosions, apparently to test depth-charge effectiveness.

The Allied technical experts found much to praise about her design and construction. Graph's auxiliary machinery was on rubber mountings, making the boat more stealthy by reducing sound transmission into the hull. The quality of her construction was excellent. Her underwater acoustic equipment was found to be a sophisticated array of hydrophone

Hydrophone

A hydrophone is a microphone designed to be used underwater for recording or listening to underwater sound. Most hydrophones are based on a piezoelectric transducer that generates electricity when subjected to a pressure change...

s that was significantly better than the British equivalents, and several design features were recommended to be copied in British and American submarines. The main criticism of the boat was poor and cramped crew accommodation, which would degrade crew performance on long patrols.

In mid-1942, Graph was carefully studied by the US Navy, which then had an interest in a new, small submarine that would be roughly her size – around half the size of the Gato class

Gato class submarine

The United States Navy Gato class submarine formed the core of the submarine service that was largely responsible for the destruction of the Japanese merchant marine and a large portion of the Imperial Japanese Navy in World War II...

boats that formed the bulk of the US submarine fleet. She was considered superiour in many ways to the two, experimental Mackerel class submarine

Mackerel class submarine

The Mackerel class submarines were a pair of experimental prototype submarines built just prior to the World War II. The two submarines were similar in size and capability to the S class submarines built at the end of World War I, and had been ordered to test the feasibility of using mass...

s, the existing class of small US Submarine, but the project was dropped.

In a highly secret British project, Graph was also used as a model for the construction of three, full-sized, mock-ups of the control compartment, wardroom and radio room of a Type VII U-boat. These were used to train specialist groups of sailors, who would form boarding parties whenever a damaged U-boat was blown to the surface. They were trained to operate a U-boat's ballast-tank valves, to reverse any scuttling attempts by the crew, and were taught where to quickly search for cryptographic equipment and documents.

Active service

On 21 October 1942, in the bay of Biscay, about 50 nautical miles (92.6 km) north-north-east of Cape Ortegal (44°31′N 7°25′W), Graph encountered the . Four torpedoes were fired but all missed. In December 1942, HMS Graph sighted the German cruiser on her return to Altenfjord following the Battle of the Barents Sea

Battle of the Barents Sea

The Battle of the Barents Sea took place on 31 December 1942 between German surface raiders and British ships escorting convoy JW 51B to Kola Inlet in the USSR. The action took place in the Barents Sea north of North Cape, Norway...

, but Hipper was travelling too fast to be attacked. Three hours later, Graph sighted one German destroyer towing a second, and attacked. However, her torpedoes missed.

Decommissioning

Defects, exacerbated by a shortage of spare parts, led to her being placed in reserve. Also, her batteries and her MAN diesel engines had a comparatively short service life; German submarine batteries required annual replacement, unlike British batteries which were intended to last for the lifetime ot the boat.

She was decommissioned from active service in February 1944. She saw some use as a target, to determine the damage caused by depth charges in full-scale trials. After surviving these experiments, on 20 March 1944, she was being towed by the tug from Aberdeen

Aberdeen

Aberdeen is Scotland's third most populous city, one of Scotland's 32 local government council areas and the United Kingdom's 25th most populous city, with an official population estimate of ....

to the Clyde

River Clyde

The River Clyde is a major river in Scotland. It is the ninth longest river in the United Kingdom, and the third longest in Scotland. Flowing through the major city of Glasgow, it was an important river for shipbuilding and trade in the British Empire....

for scrapping when her tow–rope broke. She ran aground at a position 55°48′06"N 6°28′30"W, near Coul Point, on the west coast of Islay

Islay

-Prehistory:The earliest settlers on Islay were nomadic hunter-gatherers who arrived during the Mesolithic period after the retreat of the Pleistocene ice caps. In 1993 a flint arrowhead was found in a field near Bridgend dating from 10,800 BC, the earliest evidence of a human presence found so far...

, Scotland. She was partially salvaged and scrapped in 1947. In 1966, the salvage diver Keith Jessop

Keith Jessop

Keith Jessop was a British salvage diver and successful marine treasure hunter.-Early life:Born in Keighley as the son of a penniless Yorkshire mill-worker, he left school without a single qualification, but to make ends meet he started salvaging scrap metal from shallow water wrecks off the coast...

removed some more of the wreck, but stopped work when he became involved in a court case over salvage rights. Some remains of HMS Graph remained visible at low tide on the rocks near Saligo beach in 1970, with the pressure casing of the conning tower and periscope tube clearly visible (the cladding and railings etc. all washed off in the Atlantic storms many years before). Today, the remains of the wreck lie in about 5 metres (16.4 ft) of water; the site has been visited and photographed by recreational divers.

As well as her battle flag in the RAF museum, surviving relics from the boat include her typewriter, held by the museum at Bletchley Park