Discovering H.M.S. Ark Royal
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Feature In November 1941 the aircraft carrier H.M.S. Ark Royal was returning from Malta, when it had been torpedoed and sunk by a German U-boat Southeast of Gibraltar. Its destruction was a devastating blow to the Royal Navy's power in the Mediterranean theatre of war and to the morale of the British people. In October 2002, nearly sixty- one years after it was lost, the remains of the Ark Royal were identified on the bottom of the Mediterranean using By Daniel Warren, Robert Church and Rick Davey, C & C Technologies, C & C Technologies HUGIN 3000 AUV. Inc., USA Discovering H.M.S. Ark Royal In the autumn of 2002 the British that had been converted from other In two years of wartime operations Broadcasting Corporation (BBC) con- types of warships, the Ark Royal had the Ark Royal had been attacked nu- tracted C & C Technologies, Inc. been planned from conception to be merous times but had managed to (C & C) of Lafayette, Louisiana to an aircraft carrier. Constructed in survive relatively unscathed. Howev- conduct a search for the World War Birkenhead, England, between 1935 er, on November 13th 1941, while re- II aircraft carrier H.M.S Ark Royal.The and 1938, the new carrier had an turning from operations off Malta, luck search would be carried out using C overall length of 244 metres and dis- ran out for the Ark Royal when it was & C's HUGIN 3000 AUV,which at the placed over 23,000 tons when it was sighted by Friedrich Guggenberger, time was deployed in the Mediter- commissioned in November 1938. It commander of the German subma- ranean. A key point of the project was capable of speeds of up to 31 rine U-81, who fired four torpedoes would be the investigation of a target knots and could carry up to seventy- from long range at the Ark Royal and located in 1,066 metres of water dur- two attack aircraft. In addition to its its escorting battleship.A single tor- ing a BBC-sponsored multi-beam sur- complement of aircraft, the Ark Royal pedo struck the starboard side of Ark vey search for the carrier. During a bristled with an array of defensive ar- single dive the HUGIN 3000 surveyed mament that included sixteen 4.5-inch this object with side-scan sonar, sub- guns, thirty-two 2-pounder anti-air- bottom profiler and multi-beam sys- craft guns, and thirty-two 5-inch guns. tems.The results of this survey con- Once commissioned, the Ark Royal was firmed that the target was indeed the assigned to the Royal Navy's Home wreck of the Ark Royal.This article dis- Fleet. At the outbreak of hostilities cusses the survey and its findings. with Germany in late 1939 the Ark Roy- al saw action almost immediately, its aircraft assisting in the sinking of the Historical Background first German U-boat of the war, U-39. The Ark Royal (Figure 1) was the Roy- It also shot down the first German air- al Navy's first modern aircraft carri- craft of the war.Throughout roughly er. Unlike other carriers in the Fleet the next year and a half, from October 1939 to March 1941, the Ark Roy- Figure 2: HUGIN 3000 AUV, (Photo C & C al took part in many of the ma- Technologies). jor operations in the Atlantic and Mediterranean. Among these Royal, exploding amidships, directly un- were the search for the German der the superstructure. The blast Pocket Battleship Graf Spree, the ripped a 40-metre by 9-metre deep Norway Campaign and the de- hole in the carrier, killing one British struction of the French Fleet at sailor.Within minutes the Ark Royal Dakar. In May 1941 the Ark Royal was listing heavily to starboard.The played a key role in the destruc- following morning, on 14th Novem- tion of the German Battleship ber 1941, despite all efforts to save DKM Bismarck when a torpedo the ship, the Ark Royal rolled over and from one of its Swordfish aircraft settled on the bottom of the Mediter- severely damaged the battleship's ranean, where it remained undiscov- Figure 1: H.M.S. Ark Royal (Photo Naval Historical Center). steering. ered for nearly sixty-one years. 26 - September 2004 Hydro INTERNATIONAL Feature HiPAP (High Precision er.A side-scan sonar mosaic was pro- Acoustic Positioning) duced and each line of data was re- acoustic tracking system. viewed by C & C and BBC personnel Surveying in 1,500 metres for details of the wreck site for com- of water HUGIN 3000 parison with plans of the carrier. positioning is accurate to Based on the data acquired by the ±5 metres, after post- HUGIN, the wreck site was con- processing. firmed to be that of the H.M.S.Ark Royal. The sonar mosaic (Figure 3) provides Survey and Findings an overall picture of the wreck re- The HUGIN 3000 AUV mains. It indicates that the wreck site investigation grid for the is strewn over nearly 0.27 square kilo- BBC multi-beam target metres of seafloor and is oriented was devised to provide roughly north to south.At the north- maximum coverage of ern edge of the wreck site are the the search area; it con- remnants of the main hull.Approxi- sisted of eighteen track- mately 218 metres to the south of lines approximately 1,800 metres long. The high-frequency sonar lines were de- Figure 3: High-resolution side-scan sonar mosaic of Ark signed to provide opti- Royal wreck site (Image by BBC and C & C). mum sonar-strike an- gles by programming the AUV to pass the target from HUGIN 3000 AUV three directions.The series of The C & C HUGIN (High Precision survey lines were offset in in- Untethered Geosurvey and Inspec- crements of 10 metres tion System) Autonomous Underwa- from the main target area ter Vehicle (AUV) (Figure 2) is a third- and provided coverage of generation AUV by Kongsberg Simrad a 1.6-kilometre by 1-kilo- and the first commercially operated metre area of seafloor in a AUV capable of surveying to 3,000 water depth of 1,066 me- metres water depth.This AUV is in- tres. During the survey, which tegrated with a multi-instrument sur- took approximately 7 hours, vey payload consisting of a Simrad EM the AUV maintained an altitude 2000 (200kHz) swath bathymetry sys- of approximately 20 metres above tem, dual-frequency Edgetech Chirp the bottom. Real-time acoustic links side-scan sonar (120kHz and 410kHz) with the AUV provided the first im- and an Edgetech Chirp subbottom ages of the wreck. Once the survey profiler.AUV position accuracy is ac- was completed, the data was re- complished using an inertial naviga- covered and processed onboard the these remains lies an extensive field Figure 5: Multi- tion system coupled with a Simrad AUV support vessel M/V Rig Support- of debris containing several large beam composite pieces of wreckage. image of main hull The main hull section measures 183 of Ark Royal (Image metres in length, roughly 61 metres by BBC and C & C). shorter than the recorded length of the Ark Royal.The high-resolution side-scan sonar images of the main hull (Figure 4) revealed extensive damage to the forward section, sug- gesting that a portion of the bow had ripped away, along with portions of the flight deck and the superstructure. Several of the Ark Royal's gun turrets remain intact on the wreck and are visible in the high-resolution imagery. A multi-beam composite of the hull remains (Figure 5) shows the vessel sitting relatively upright, with only 10 metres of bottom relief, indicating Figure 4: High-resolution side-scan sonar image of main hull of Ark Royal (Image by BBC that much of the lower hull is em- and C & C). bedded in the seafloor. Displaced sed- Hydro INTERNATIONAL September 2004 - 27 Feature Figure 8: wreck of one of Britain's most famous High-resolution warships.This study provided insight sonar image of into the last moments of this illustri- remains of Ark Figure 6: High-resolution side-scan sonar image of possible Swordfish aircraft in field of ous vessel and opened the door to Royal debris (Image by BBC and C & C). future research opportunities. superstructure (BBC and C & C). iments visible in the multi-beam im- fish biplane (Figure 6).At the south- agery provide evidence that the im- ern extremity of the field is a large Biographies pact of the hull as it entered the section of debris partially buried in Daniel Warren is staff marine archae- seabed was in a south to north di- the seafloor.This appears to be the ologist for C & C Technologies,Inc., rection. remnants of the missing bow section at the Houston,Texas office and has Lying south of the main hull by 218 (Figure 7) with one of the aerial lift an MA degree in Maritime History metres is a 527-metre long by 426- arms still attached. and Nautical Archaeology. He was metre wide field of debris (Figure 3). principle investigator for the 2003 U- High-resolution side-scan imagery de- 166 Archaeological Project and is co- picted a wide variety of objects scat- Conclusions principle investigator for the 2004 tered throughout this area, including Based on the findings of the HUGIN Deep Gulf Shipwreck Project. pieces of the superstructure, flight 3000 AUV survey of the Ark Royal Robert Church is staff marine ar- deck remains, gun turrets and sever- wreck site it is possible to speculate chaeologist for C & C Technologies, al aircraft.