Editing Depth charge (section)

==History==
[[File:USS Cassin Young depth charges.jpg|thumb|Depth charges on {{USS|Cassin Young|DD-793}}]]

The first attempt to fire charges against submerged targets was with aircraft bombs attached to lanyards which triggered them. A similar idea was a {{cvt|16|lb}} [[guncotton]] charge in a lanyarded can. Two of these lashed together became known as the "depth charge Type A".<ref>{{Harvnb|McKee|1993|p=46}}</ref> Problems with the lanyards tangling and failing to function led to the development of a chemical pellet trigger as the "Type B".<ref name="m49">{{Harvnb|McKee|1993|p=49}}</ref> These were effective at a distance of around {{cvt|20|ft|m|sigfig=1}}.<ref name="m49"/>

A 1913 Royal Navy Torpedo School report described a device intended for [[Demining|countermining]], a "dropping mine". At Admiral [[John Jellicoe]]'s request, the standard Mark II mine was fitted with a [[hydrostatic]] pistol (developed in 1914 by Thomas Firth and Sons of Sheffield) preset for {{cvt|45|ft}} firing, to be launched from a stern platform. Weighing {{cvt|1150|lb}}, and effective at {{cvt|100|ft}}, the "cruiser mine" was a potential hazard to the dropping ship.<ref name="m49"/> The design work was carried out by Herbert Taylor at the RN Torpedo and Mine School, [[HMS Vernon (shore establishment)|HMS ''Vernon'']]. The first effective depth charge, the Type D, became available in January 1916. It was a barrel-like casing containing a high [[explosive]] (usually [[trinitrotoluene|TNT]], but [[amatol]] was also used when TNT became scarce).<ref name="m49"/> There were initially two sizes—Type D, with a {{cvt|300|lb}} charge for fast ships, and Type D* with a {{cvt|120|lb}} charge for ships too slow to leave the danger area before the more powerful charge detonated.<ref name="m49"/><ref name="t27">{{harvnb|Tarrant|1989|p=27}}</ref>

A hydrostatic pistol actuated by water pressure at a pre-selected depth [[detonate]]d the charge.<ref name="t27"/> Initial depth settings were {{cvt|40|or|80|ft}}.<ref name="t27"/> Because production could not keep up with demand,<ref name="m50">{{Harvnb|McKee|1993|p=50}}</ref> anti-submarine vessels initially carried only two depth charges, to be released from a chute at the stern of the ship.<ref name="t27"/> The first success was the sinking of [[SM U-68|''U-68'']] off [[County Kerry]], Ireland, on 22 March 1916, by the [[Q-ship]] [[HMS Farnborough|''Farnborough.'']]<ref name="t27"/> Germany became aware of the depth charge following unsuccessful attacks on [[SM U-67|''U-67'']] on 15 April 1916, and [[SM U-69|''U-69'']] on 20 April 1916.<ref name="t27"/> The only other submarines sunk by depth charge during 1916 were [[SM UC-19|''UC-19'']] and [[SM UB-29|''UB-29'']].<ref name="t27"/>

Numbers of depth charges carried per ship increased to four in June 1917, to six in August, and 30–50 by 1918.<ref name="m50"/> The weight of charges and racks caused ship instability unless heavy guns and torpedo tubes were removed to compensate.<ref name="m50"/> Improved pistols allowed greater depth settings in {{cvt|50|ft}} increments, from {{cvt|50|to|200|ft}}.<ref name="m49"/><ref name="t40">{{harvnb|Tarrant|1989|p=40}}</ref> Even slower ships could safely use the Type D at below {{cvt|100|ft}} and at {{cvt|10|kn|km/h mph}} or more,<ref name="m50"/> so the relatively ineffective Type D* was withdrawn.<ref name="t40"/> Monthly use of depth charges increased from 100 to 300 per month during 1917 to an average of 1745 per month during the last six months of [[World War I]].<ref name="t40"/> The Type D could be detonated as deep as {{cvt|300|ft|m|sigfig=1}} by that date. By the war's end, 74,441 depth charges had been issued by the RN, and 16,451 fired, scoring 38 kills in all, and aiding in 140 more.<ref name="m50"/>

[[File:HMS Ceylon depth charge.jpg|thumb|Depth charge exploding after being released by [[HMS Ceylon (30)|HMS ''Ceylon'']]]]

The United States requested full working drawings of the device in March 1917. Having received them, Commander Fullinwider of the U.S. Bureau of Naval Ordnance and U.S. Navy engineer Minkler made some modifications and then patented it in the U.S.<ref>{{cite patent |country=US |number=1321428 |title=Horn Mine |inventor1-last=Fullinwider |inventor1-first=Simon P. |inventor2-last=Minkler |inventor2-first=Chester T. |pubdate= 1919-11-17 |fdate=1917-11-11 |assign=[[United States Government]] }}</ref> It has been argued that this was done to avoid paying the original inventor.<ref>{{Citation |title=Museum Discovers Unknown Inventor |publisher=Explosion – Museum of Naval Firepower |url=http://www.explosion.org.uk/index.php?option=com_content&view=category&layout=blog&id=57&Itemid=222&limitstart=42 |access-date=29 September 2012 }}</ref><ref>{{Citation |last=Prudames |first=David |title=Inventor Of The Depth Charge Discovered At Explosion! |date=20 August 2003 |location=Brighton, UK |publisher=Culture24 |access-date=29 September 2012 |url=http://www.culture24.org.uk/history+%26+heritage/war+%26+conflict/art17861 |archive-date=29 September 2012 |archive-url=https://web.archive.org/web/20120929101420/http://www.culture24.org.uk/history+%26+heritage/war+%26+conflict/art17861 |url-status=dead }}</ref>

The Royal Navy Type D depth charge was designated the "Mark VII" in 1939.<ref name="campbell">{{harvnb|Campbell|1985|p=89}}</ref> Initial sinking speed was {{cvt|7|ft/s}} with a terminal velocity of {{cvt|9.9|ft/s}} at a depth of {{cvt|250|ft}} if rolled off the stern, or upon water contact from a depth charge thrower.<ref name="campbell"/> Cast iron weights of {{cvt|150|lb}} were attached to the Mark VII at the end of 1940 to increase sinking velocity to {{cvt|16.8|ft/s}}.<ref name="campbell"/> New hydrostatic pistols increased the maximum detonation depth to {{cvt|900|ft}}.<ref name="campbell"/> The Mark VII's {{cvt|290|lb}} amatol charge was estimated to be capable of splitting a {{cvt|7/8|inch|mm}} submarine pressure hull at a distance of {{cvt|20|ft|m|sigfig=1}}, and forcing the submarine to surface at twice that.<ref name="campbell"/> The change of explosive to [[Torpex]] (or Minol) at the end of 1942 was estimated to increase those distances to {{cvt|26|and|52|ft|m|0}}.<ref name="campbell"/>

The British Mark X depth charge weighed {{cvt|3000|lb}} and was launched from the {{cvt|21|in}} [[torpedo tube]]s of older destroyers to achieve a sinking velocity of {{cvt|21|ft/s}}.<ref name="campbell"/> The launching ship needed to clear the area at 11 knots to avoid damage, and the charge was seldom used.<ref name="campbell"/> Only 32 were actually fired, and they were known to be troublesome.<ref>{{Harvnb|McKee|1993|p=53}}</ref>

The teardrop-shaped United States Mark 9 depth charge entered service in the spring of 1943.<ref name="c163">{{harvnb|Campbell|1985|p=163}}</ref> The charge was {{cvt|200|lb}} of Torpex with a sinking speed of {{cvt|14.4|ft/s}} and depth settings of up to {{cvt|600|ft}}.<ref name="c163"/> Later versions increased depth to {{cvt|1000|ft}} and sinking speed to {{cvt|22.7|ft/s}} with increased weight and improved streamlining.<ref name="c163"/>

Although the explosions of the standard United States {{cvt|600|lb}} Mark 4 and Mark 7 depth charge used in World War II were nerve-wracking to the target, a U-boat's pressure hull would not rupture unless the charge detonated within about {{cvt|15|ft|m|0}}. Getting the weapon within this range was a matter of luck and quite unlikely as the target took evasive action. Most U-boats sunk by depth charges were destroyed by damage accumulated from an extended barrage rather than by a single charge, and many survived hundreds of depth charges over a period of many hours, such as [[Unterseeboot 427|''U-427'']], which survived 678 depth charges in April 1945.