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[[File:Torpedo exploder Mark 6 early.jpg|right|thumb|Mark 6 exploder. This version apparently does not have a voltage regulator.]]

The '''Mark 6 exploder''' was a [[United States Navy]] [[torpedo]] [[exploder]] developed in the 1920s. It was the standard exploder of the Navy's [[Mark 14 torpedo]] and [[Mark 15 torpedo]].{{efn|The similar [[Mark 13 torpedo]] used Mark 4 or Mark 8 exploders.<ref name="OP 629(A)">{{cite book | url=http://www.maritime.org/doc/torpedomk13/torp003.htm | title = Torpedo Mark 13, OP 629(A), Description, Adjustment, Care, and Operation | work = Maritime | publisher = [[United States Navy]] | date = July 1942}}</ref><ref name= "navyhist">{{cite web | work = Keyport museum | title = Torpedo History: Torpedo Mk 13 | url = http://www.history.navy.mil/museums/keyport/html/part2.htm | publisher = Navy | access-date = 2013-06-05 | archive-date = 2014-09-15 | archive-url = https://web.archive.org/web/20140915054904/http://www.history.navy.mil/museums/keyport/html/part2.htm  }}</ref>}}

==Development==
[[File:Torpedo Exploder Mark 6 NH-88457.jpg|thumb|A failed 1926 test shot.]]
[[File:Torpedo exploder Mark 6 Mod 1.jpg|right|thumb|Defective, inadequately tested Mark 6 Mod 1 exploder used early in the war.<ref>{{Citation |last=Patrick |first=John |title=The Hard Lessons of World War II Torpedo Failures |journal=Undersea Warfare |date=Winter 2012 |issue=47 |url=http://www.public.navy.mil/subfor/underseawarfaremagazine/issues/archives/issue_47/torpedo_2.html |access-date=2013-06-22 |archive-url=https://web.archive.org/web/20141013151521/http://www.public.navy.mil/subfor/underseawarfaremagazine/issues/archives/issue_47/torpedo_2.html |archive-date=2014-10-13  }}</ref> In September 1943, it was replaced with the Mark 6 Mod 5.<ref>{{harvnb|Milford|1996b}}</ref>]]

Early torpedoes used [[contact exploders]]. A typical exploder had a firing pin that stuck out from the warhead and was restrained by a transverse shear pin. The torpedo would hit the target with enough energy to break the shear pin and allow the firing pin to strike a percussion cap that ultimately detonated the warhead. An arming impeller was an additional safety device: the firing pin could not move until the torpedo had traveled a preset distance.<ref name="WP 63">{{harvnb|Wildenberg|Polmar|2010|p=63}}</ref>

Just before World War I, the [[Bureau of Ordnance]] (commonly called BuOrd) started developing an inertial exploder. The result was the [[Mark 3 exploder]].<ref name="WP 63"/>

Warships employed defenses against torpedoes. A new technology, [[Anti-torpedo bulge|torpedo blisters]], appeared on [[capital ship]]s. The torpedo would explode against the blister but do little damage to the hull. Torpedo blisters were tested on two battleships, the decommissioned {{USS|South Carolina|BB-26|2}} and the unfinished {{USS|Washington|BB-47|2}}; the conclusion was the [[Mark 10 torpedo]], with its contact exploder, could not disable a major warship.<ref>{{Harvnb|Wildenberg|Polmar|2010|p=64}}</ref> Torpedoes would need to explode underneath a capital ship, where there were no blisters or other armor.<ref name="Blair, p.54"/> The [[Mark 14 torpedo]] was designed at the [[Naval Torpedo Station|Newport Torpedo Station]] (NTS), [[Newport, Rhode Island|Newport]], to replace the Mark 10, which had been in service since [[World War I]]. Its fairly small {{convert|643|lb|kg|abbr=on}} warhead<ref name="Blair, p.278">{{Harvnb|Blair|1975|p=278}}</ref> required it to explode beneath the [[keel]] where there was no armor.<ref name="Blair, p.54"/>

This led to the development of a [[magnetic influence]] feature, similar to the British [[Duplex exploder|Duplex]]<ref>Fitzsimons, Bernard, general editor. ''The Illustrated Encyclopedia of 20th Century Weapons and Warfare'' (London: Phoebus Publishing, 1978), Volume 8, p.807, "Duplex"</ref> and German<ref>Dönitz, ''Memoir''.</ref> models, all inspired by German [[magnetic mine]]s of World War I.<ref name="Blair, p.54">{{Harvnb|Blair|1975|p=54}}</ref> The Mark&nbsp;6 was intended to fire the warhead beneath  the ship, creating a huge gas bubble which would cause the keel to fail catastrophically.{{citation needed|date=July 2015|reason=true, but let's cite it}}

The Mark 6 exploder, designated Project G53,<ref name="Blair, p.55">{{Harvnb|Blair|1975|p=55}}</ref> was developed "behind the tightest veil of secrecy the Navy had ever created."<ref name="Blair, p.55"/> In less than two years, [[Newport Torpedo Station]] produced a prototype with help from [[General Electric]]. The prototype exploder was fitted to a Mark 10 torpedo and test-fired in [[Narragansett Bay]] on 8 May 1926; the submarine {{USS|L-8|SS-48|6}} was the target.<ref>{{harvnb|Wildenberg|Polmar|2010|pp=64–65}}</ref>

In the first test, the torpedo ran underneath the target submarine but did not explode; a second test was successful.  Those two shots were the only live-fire tests until World War II. After several redesigns, General Electric in [[Schenectady, New York|Schenectady]] made 30 production units, at a cost of [[United States dollar|US$]]1,000 apiece.<ref>{{Harvnb|Blair|1975|p=61}}</ref>{{inflation-fn|US}}<ref>{{harvnb|Wildenberg|Polmar|2010|p=65}}</ref> The exploder was tested at the Newport lab and in a small field test aboard {{USS|Raleigh|CL-7|6}}.

At the urging of Lt. [[Ralph Waldo Christie|Ralph W. Christie]], who headed the Mark 14's design team, equatorial tests were later conducted by {{USS|Indianapolis|CA-35|6}}, which fired one hundred trial shots between 10°N and 10°S<ref name="Blair 1975 61–62">{{Harvnb|Blair|1975|pp=61–62}}</ref> and collected 7,000&nbsp;readings.<ref name="Blair, p.62">{{Harvnb|Blair|1975|p=62}}</ref> The tests were done using torpedoes with instrumented exercise heads: an electric eye would take an upward-looking picture from the torpedo; the magnetic influence feature would set off some [[gun cotton]].<ref name="Blair 1975 61–62"/>

Due to budgetary constraints, very few live-fire trials of the torpedo or exploder were ever conducted. The goal of most exercise firings was to get the torpedo to run under the target, after which it was assumed the magnetic influence feature would do the work. This misplaced trust in the magnetic exploder helped mask the depth problems encountered by early torpedoes, for if the exploder were to work properly a depth error of a few feet would not matter.<ref name="Morison IV">Morison, Samuel E. ''History of United States Naval Operations in World War II, volume IV'', ''passim''</ref> [[Chief of Naval Operations]] [[William V. Pratt]] offered the [[Hulk (ship type)|hulk]] of {{sclass|Cassin|destroyer}} {{USS|Ericsson|DD-56|6}},<ref name="Blair, p.62"/><ref>Fitzsimons, Volume 5, p.541, table.</ref> but prohibited the use of a live warhead, and insisted BuOrd pay the cost of refloating her if she was hit in error.<ref name="Blair, p.62"/> These were strange restrictions, as ''Ericsson'' was due to be scrapped.<ref>Between 1934 and 1936. Fitzsimons, Volume 5, p.542, "''Cassin''".</ref> BuOrd declined.<ref name="Blair, p.62"/> A service manual for the exploder "was written—but, for security reasons, not printed—and locked in a safe."<ref name="Blair, p.62"/>

==Problems==
[[File:Torpedo Exploder Mark 6 NH Drawing.png|upright|thumb|Mechanical drawing of the Mark6 Mod 1 exploder.]]

After the Mark 14 entered combat service in the [[Pacific War]], it was discovered the torpedo had several major flaws. Two of these were directly related to the Mark 6 exploder:
* It often caused premature firing.
* The contact pistol frequently failed to fire the warhead. It often jammed with a textbook right angle hit to a ship's side as the firing pin could not take the shock of the impact.

Similar problems also plagued the [[Mark 15 torpedo]] used by U.S. Navy [[destroyer]]s. The problems could lead to misses or failures, and tended to mask one another, making isolating any one of them more difficult.<ref name="Morison IV" />{{page needed|date=August 2015}}

===Premature explosions===
[[File:Mk6-mag-exploder.gif|left|thumb|Later model of the Mark 6 magnetic exploder assembly that uses a ball switch assembly as the contact exploder. The ball switch did not have the high acceleration problems of the earlier models.]] 
Many submarine commanders in the first two years of the war reported explosions of the warhead with little to no damage of the enemy. The magnetic exploders were triggering prematurely, before getting close enough to the vessel to destroy it. Earth's magnetic field near NTS, where the trials (limited as they were)<ref>Milford, Frederick J. "U. S. Navy Torpedoes." ''The Submarine Review'', April 1996.</ref> were conducted, differed from the areas where the fighting was taking place.

===Duds===
Early reports of torpedo action included some dud hits, heard as a dull clang. In a few instances, Mark&nbsp;14s would strike a Japanese ship and lodge in its hull without exploding. The contact pistol appeared to be malfunctioning, though the conclusion was anything but clear until running depth and magnetic exploder problems were solved. This experience was exactly the sort of live-fire trial BuOrd had been prevented from doing in peacetime, causing one submarine skipper to complain, "[Making] round trips of {{convert|8500|mi|km}} into enemy waters to gain attack positions undetected within {{convert|800|yd|m}} of enemy ships only to find that torpedoes run deep and over half the time fail to function, seems to me an undesirable method of gaining information which might be determined any morning within a few miles of a torpedo station in the presence of comparatively few hazards."<ref name="Morison IV" /> It was now clear to all at Pearl Harbor that the contact pistol was also defective.

==Solutions==

Against orders, some submariners disabled the magnetic influence feature of the Mark&nbsp;6 exploder, suspecting it was faulty. An increase in hits was reported. Shortly after replacing Wilkes in Fremantle,<ref name="Blair, p.274">{{Harvnb|Blair|1975|p=274}}</ref> [[Rear Admiral]]<ref name="Blair, p.274"/> [[Charles A. Lockwood|Charles Lockwood]] ordered a historic net test at [[Frenchman Bay (Australia)|Frenchman Bay]] on 20&nbsp;June 1942.<ref name="Blair, p.275">{{Harvnb|Blair|1975|p=275}}</ref> Eight hundred Mark 14s had already been fired in combat.<ref name="Blair, p.275"/>

After a historic net test by [[James W. Coe|Jim Coe]]'s {{USS|Skipjack|SS-184|2}}, BuOrd on 1&nbsp;August 1942 finally conceded the Mark&nbsp;14 ran deep, and six weeks later, "that its depth-control mechanism had been 'improperly designed and tested'".<ref name="Blair, p.278"/> This satisfied Lockwood and [[Robert Henry English|Robert H. English]] (then [[ComSubPac|<small>COMSUBPAC</small>]]),<ref>{{Harvnb|Blair|1975|pp=226–227}}</ref> who both refused to believe the exploder could also be defective.<ref name="Blair, p.278"/>

Finally, in July 1943, Admiral Lockwood (by then <small>COMSUBPAC</small>) ordered his boats to deactivate the Mark&nbsp;6's influence feature and use only its contact pistol.<ref name="historynet.com">[http://www.historynet.com/magazines/world_war_2/3037866.html Shireman, Douglas A. ''U.S. Torpedo Troubles During World War II''] {{webarchive|url=https://web.archive.org/web/20080228231018/http://www.historynet.com/magazines/world_war_2/3037866.html |date=2008-02-28 }}</ref>

Tests were carried out by <small>COMSUBPAC</small>'s gunnery and torpedo officer, [[Arthur Howard Taylor|Art Taylor]] (ex-{{USS|Haddock|SS-231|2}}). Taylor, [[Charles Momsen|"Swede" Momsen]], and others fired warshots from {{USS|Muskallunge|SS-262|2}}<ref>Under command of Willard Saunders. {{Harvnb|Blair|1975|p=437}}</ref> into the cliffs of [[Kahoolawe]], beginning 31&nbsp;August. Their third test shot was a dud.<ref name="Blair, p.437">{{Harvnb|Blair|1975|p=437}}</ref> This revealed the firing pin had not been able to contact the detonator hard enough to fire the warhead.<ref name="Blair, p.437"/>

To avoid "shaking hands with St. Peter" (as Lockwood put it),<ref name="Blair, p.437"/> E.A. Johnson, [[United States Navy Reserve|USNR]], supervised by Taylor, dropped dummy warheads filled with sand from a crane raised to a height of {{convert|90|ft}}. In 7 out of 10 of these trials, firing mechanisms bent, jammed, and failed with the high inertia of a straight-on hit (the prewar ideal).<ref name="Blair, p.438">{{Harvnb|Blair|1975|p=438}}</ref> A quick fix was to encourage "glancing" shots<ref name="Blair, p.439">{{Harvnb|Blair|1975|p=439}}</ref> (which cut the number of duds in half),<ref name="Blair, p.438"/> until a permanent solution could be found. Lightweight aluminum alloy (from propellers<ref name="Blair, p.438"/> of Japanese planes shot down during the [[attack on Pearl Harbor]]) was machined to take the place of the Mark&nbsp;6's heavy pin block so inertial forces would be lower. Electrical switches, developed by Johnson,<ref name="Blair, p.438"/> were tried as well. Both fixes worked and were relatively easy to implement. In September 1943, the first torpedoes with new contact pistols were sent to war.<ref>{{citation |url=http://www.geocities.com/Pentagon/1592/ustorp2.htm |archive-url=https://web.archive.org/web/20091023091106/http://geocities.com/Pentagon/1592/ustorp2.htm |archive-date=2009-10-23  |last=Milford |first=Frederick J. |title=U. S. Navy Torpedoes. Part Two: The great torpedo scandal, 1941–43. |journal=The Submarine Review |date=October 1996b}}</ref> "After twenty-one months of war, the three major defects of the Mark&nbsp;14 torpedo had at last been isolated. ... Each defect had been discovered and fixed in the field—always over the stubborn opposition of the Bureau of Ordnance."<ref name="Blair, p.439"/>

==See also==
*[[Naval mine#Influence mines|Magnetic mine]]

==References==
===Footnotes===
{{Notelist}}

===Notes===
{{Reflist}}

===Bibliography===
{{Refbegin}}
* {{Citation |last=Blair |first=Clay Jr. |title=Silent Victory |location=Philadelphia |publisher=Lippincott |year=1975 |isbn=0-553-01050-6}}
* {{Citation |last=Roscoe |first=Theodore |title=Pig Boats: The True Story of the Fighting Submariners of World War II |location=New York |publisher=Bantam |year=1967 |oclc=22066288 }}. Originally published in 1949 as ''United States submarine operations in World War II''; Bantam version may be abridged.
* [http://www.navweaps.com/Weapons/WTUS_WWII.htm United States of America Torpedoes of World War II]
* {{Citation |last1=Wildenberg |first1=Thomas |last2=Polmar |first2=Norman |title=Ship Killer: A History of the American Torpedo |year=2010 |location=Annapolis, MD |publisher=Naval Institute Press |isbn=978-1-59114-688-9}}
{{Refend}}

==Further reading==
* {{Citation | last=Gannon | first=Robert | title=Hellions of the Deep: The Development of American Torpedoes in World War II | publisher=Pennsylvania State University Press | year=1996 | isbn=0-271-01508-X |ref=none}}
* {{Citation
  | last = Newpower | first = Anthony 
  | year = 2010
  | title = Iron Men and Tin Fish: The Race to Build a Better Torpedo During World War II 
  | publisher = Naval Institute Press | location = Annapolis, Md
  | isbn = 978-1-59114-623-0 |ref=none}}
* {{Citation |title=Instructions for upkeep & Operation of the Mark VI Mod. 1 exploder mechanism |publisher=Bureau of Ordnance |series=Ordnance Pamphlet |year=1938 |id=OP 632 |oclc=51958048 }}

==External links==
* {{cite web | url=http://www.ww2pacific.com/torpedo.html | title=Dud Torpedoes | publisher=World War II in the Pacific}}
* {{cite web | url= http://diodon349.com/Torpedoman/Torpedoes_USN/mark_14_3A_torpedo_Mk_6_exploder.htm
 |title= Mark 14-3A Torpedo and its MK 6 Exploder 
 |access-date= 3 March 2012 | url-status= usurped
 |archive-url=https://web.archive.org/web/20041013135156/http://www.diodon349.com/Torpedoman/Torpedoes_USN/mark_14_3A_torpedo_Mk_6_exploder.htm |archive-date=13 October 2004}}
* {{cite web | url=http://www.maritime.org/wish/exploder.htm | title=Mark 6 Magnetic Exploder Mechanism (images) | publisher=San Francisco Maritime National Park Association | access-date=21 July 2015}}
* {{cite letter | first=Albert | last=Einstein | author-link=Albert Einstein | recipient=Commander Stephen Brunauer, U.S. Navy Bureau of Ordnance | subject=Torpedo before explosion | url=https://research.archives.gov/id/305254 | date=4 January 1944 |ref=none}} describing problem of deceleration of torpedo, recognizing the deceleration would destroy the torpedo, and suggesting an empty space in front of torpedo "to gain a few thousands of a second" in which to detonate the warhead.
* {{cite book | first=József | last=Illy | title=The Practical Einstein: Experiments, Patents, Inventions | date=2012 | publisher=The Johns Hopkins University Press | location=Baltimore | url=https://books.google.com/books?id=EoMixQWUj6oC&pg=PA161 | page=163| isbn=978-1-4214-0457-8 |ref=none }} [[John Bardeen]] also involved.
* {{cite web |last1=Schwarz |first1=Frederic D. |title=Einstein's Ordnance |url=http://www.inventionandtech.com/content/einstein%E2%80%99s-ordnance-1 |website=Invention & Technology |access-date=10 November 2022 |date=Spring 1998 |ref=none}}
* {{cite web | url=http://motls.blogspot.com/2012/11/albert-einstein-destroyed-37-hitlers.html | title=Einstein destroyed 37 Hitler's submarines | date=November 2012 | first=Luboš | last=Motl | publisher=the reference frame (blog) |ref=none}} Einstein and the acoustic torpedo.
* {{cite book | first=Russell Sydnor Jr. | last=Crenshaw | title=South Pacific Destroyer: The Battle for the Solomons from Savo Island to Vella Gulf | page=154 | date=1998 | publisher=Naval Institute Press | location=Annapolis | isbn=978-1-61251-550-2 | url=https://books.google.com/books?id=vb_QAwAAQBAJ&pg=PT154 |ref=none}} Mark 6 was not just a sub problem. Claims Mark 15 had speed of 45 knots.
* {{cite book | first=Francis | last=Pike | title=Hirohito's War: The Pacific War, 1941–1945 | publisher=Bloomsbury Publishing Plc | date=2015 | isbn=978-1-4725-9673-4 | url=https://books.google.com/books?id=SfTQDAAAQBAJ&q=einstein&pg=PT4 |ref=none}} Talks about depth setting problem (as early as 1938), but also Einstein and exploder; timing is generous in Einstein's favor.
* {{cite report | last1=Gundersen | first1=Charles R. | last2=Armstrong | first2=Jerry E. | title=The Mark 6 magnetic influence exploder: a little premature | date=April 26, 2012 | location=Keyport, WA | publisher=[[Naval Undersea Museum]] | oclc=816122607 |ref=none}}
** {{cite web | url=https://issuu.com/reprospace/docs/num_q3_fall_2013 | title=History of the Howell Torpedo | work=Undersea Quarterly | pages=1, 12 |ref=none}} Fall 2013. Naval Undersea Museum figures.
** {{cite web | url=https://issuu.com/reprospace/docs/num_q4_winter_2013 | title=The Mark 6 magnetic influence exploder: a little premature | work=Undersea Quarterly | pages=7–13 |ref=none}} Winter 2013. Excerpts from the original report.
* {{cite web | url=https://catalog.archives.gov/id/6042930 | title=S75(1) Mark 6-1 Exploders | date=1943 | publisher=Department of the Navy, U.S. Pacific Fleet | work=Confidential and Secret General Administrative Files, ca 1/1943–5/1945 |ref=none}}
* {{cite book |title=Torpedoman's Mate 3 & 2 |volume=1 |date=1955 |publisher=Government Printing Office |location=Washington |pages=196–205 |url=http://catalog.hathitrust.org/Record/006110744 |access-date=10 November 2022}}
* {{cite web |last=Drachinifel |url=https://www.youtube.com/watch?v=k7LKQBdXsHk |title=The USN Pacific Submarine Campaign - Hey, the torpedoes are working now! (Jul'43 - Dec'43) | website=[[YouTube]] |date=2023-11-15 |ref=none}} (Has images of Lockwood's drop tests)
* {{cite journal |url=https://www.usni.org/magazines/naval-history-magazine/2021/october/pieces-past |last=Blazich Jr. |first=Frank A. |title=Pieces of the Past |date=October 2021 |ref=none |journal=Naval History Magazine |publisher=U.S. Naval Institute}}

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[[Category:Torpedoes of the United States]]
[[Category:World War II naval weapons]]
[[Category:Military equipment introduced in the 1920s]]