View source for United Defense M42

{{Use American English|date=October 2024}}
{{Use dmy dates|date=October 2024}}
{{Infobox weapon
|name= United Defense M42
| image= United Defence M42.jpg
| image_size = 300
|caption= UD M42 submachine gun
|origin=United States
|type=[[Submachine gun]]
<!-- Type selection -->
|is_ranged= yes
<!-- Service history -->
|service= 1942-1945
|used_by= See [[United Defense M42#Users|Users]]
|wars= {{ubl|[[World War II]]|[[Chinese Civil War]]}}
<!-- Production history -->
|designer= Carl G. Swebilius
|design_date=
|manufacturer= United Defense Supply Corp.
|production_date= 1942–1943
|number= 15,000
|variants=
<!-- General specifications -->
|weight= {{convert|4.54|kg|lbs|sigfig=3|abbr=on}}
|length= {{convert|820|mm|in|sigfig=3|abbr=on}}
|part_length= {{convert|279|mm|in|sigfig=3|abbr=on}}
|width=
|height=
|crew=
<!-- Ranged weapon specifications -->
|cartridge=
|caliber=[[9×19mm Parabellum]]<br>[[.45 ACP]] (Prototype model)
|action= Blowback
|rate= 700 rpm to 1000 rpm
|velocity=1,100 ft/s (335.3 m/s)
|range=
|max_range=
|feed=25-round [[box magazine]] (also issued with two 25-round magazines welded face-to-face)
|sights= fixed front post, rear adjustable for windage
}}

The '''United Defense M42''', sometimes known as the '''Marlin''' for the company that did the actual manufacturing, was an American [[submachine gun]] used during [[World War II]]. It was produced from 1942 to 1943 by United Defense Supply Corp. for possible issue as a replacement for the [[Thompson submachine gun]] and was used by [[Office of Strategic Services]] (OSS) agents.<ref>{{Cite book
  | last = Bishop
  | first = Chris
  | author-link =
  | title = The Encyclopedia of Weapons of World War II
  | place = New York
  | publisher = Orbis Publishing Ltd.
  | year = 1998
  | volume =
  | edition =
  | url =
  | doi =
  | id =
  | isbn = 0-7607-1022-8
  }}.</ref> However, its usage was limited, and the Thompson continued to see service until the end of the war, alongside the [[M3 submachine gun]], which was designed around the same time as the M42.

==History==
[[File:PeterJouvenalBBCcamerman.JPG|thumb|A BBC reporter inspecting an M42 at [[Kabul]], [[Afghanistan]] in 2005.]]

The M42 submachine gun was designed by Carl G. Swebilius of the High Standard Manufacturing Company in 1940. When High Standard was tasked with producing [[.50 BMG]] machine guns for the British government, further development of the submachine gun was handled the United Defense Supply Corporation founded by Pope and Jackson of the British Purchasing Commission. United Defense did not have any manufacturing capability so it contracted with [[Marlin Firearms]] to have the M42 actually built.

The UD M42 was promoted as a replacement for the [[Thompson submachine gun]], which the U.S. military considered expensive and complicated to produce. Early model Thompson drum magazines were heavy and made a rattling sound when soldiers moved around with the weapon.  Prototypes were made in [[9×19mm Parabellum]] and [[.45 ACP|.45&nbsp;ACP]], but only the 9mm version was mass-produced. During the last three years of World War II about 15,000 9mm submachine guns were manufactured,<ref>{{cite journal |last1=Canfield |first1=Bruce N. |year=2006 |title=M42 UD (United Defense) Submachine Gun |journal=[[American Rifleman]] |volume=154 |issue=September |pages=26&27 |publisher=National Rifle Association of America}}</ref> only six .45&nbsp;ACP prototype test guns were made.

The weapon comes with a 25-round [[Magazine (firearms)|magazine]] (20-round for the .45&nbsp;ACP prototypes) designed by John E. Owsley, covered by patent 2,289,067.<ref name="magazine-patent">{{cite web |author1=J.E. Owsley |title=Patent 2,289,067 - Box-Magazine for Firearms |url=https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/2289067 |website=United States Patent & Trademark Office |access-date=4 May 2023 |pages=1 |language=English |format=PDF |date=7 July 1942 }}</ref>
Frequently two 25-round magazines were [[Jungle style (firearm magazines)|welded face-to-face]] allowing a quick reload when the first became empty.
It has a cyclic rate of 700 rounds per minute. Just like with the [[Sten submachine gun|Sten]], resistance fighters were instructed to fire in short bursts when firing in full automatic to reduce the risk of overworking the weapon that would cause jamming and overall keeping it in a good condition. They were also strongly advised to keep the double magazine clear of grass, mud, dirt and any other debris out because of the risk of jamming.
The weapon weighs {{convert|10|lb|kg|2|abbr=on}} when empty, with a length of {{convert|32.3|in|mm|0|abbr=on}}. The barrel length is {{convert|11|in|mm|0|abbr=on}}, and it has six-groove right-hand [[rifling]].

An extremely simple design, it was a [[Blowback (arms)|straight blowback]], [[selective fire]] weapon. It was built under "hurry-up" war conditions and some of its design flaws stem from this approach. Problems with the weapon were varied. Under combat conditions it was found that the sheet metal magazines had a tendency to warp out of shape causing feeding problems. They had little tolerance for exposure to large amounts of mud and sand and tended to jam if not cleaned regularly. The gun was also labor-intensive to produce. It used all machined parts, no stampings, and under wartime conditions, machine work is at a premium. However, proving ground tests showed it was easier to field strip and maintain than the Thompson or Sten Mark II and was more accurate at 300 feet/100 yards (91 m). Despite its expense and precision, the UD M42 enjoyed a good reputation when used by OSS and resistance alike.

The War Department was interested in purchasing large quantities of the M42, but due to complicated legal issues, manufacturing rights, and royalties, only 15,000 units were purchased. The M42 submachine gun was classified as a substitute standard when the [[M3 submachine gun]] was introduced.

==Operational use==
Intended for use by [[United States Armed Forces|U.S. military]] at the time of its design, it found more favor being air-dropped to [[Resistance during World War II|partisan forces]] in [[occupied Europe]]. The weapon was air dropped to supply British-led partisan forces on the island of [[Crete]], where it was used extensively. It also saw use among the partisan forces of the Italian, Belgian, Dutch, Danish, Norwegian and [[French Resistance]]. At least 4,000 sent to [[United States Navy]] installations in the Far East were transferred to [[Dai Li]]'s regular resistance forces in China for use against the [[Second Sino-Japanese War|Japanese invasion]]; and some later equipped Communist Chinese soldiers.<ref>{{cite journal |last=Parker |first=Michael J. |year=2022 |title=The UD M.'42 |journal=[[American Rifleman]] |volume=170 |issue=10 |pages=70–73 |publisher=National Rifle Association of America}}</ref> The United Defense M42 was issued for use by Filipino troops under the [[Philippine Army]] and [[Philippine Constabulary]] during World War II from 1942 through the Post-World War II era until the 1960s and was used by the local recognized guerrillas from 1942 to 1945 during the Japanese Occupation.{{citation needed|date=September 2014}} In Europe, the use of the 9mm caliber allowed resistance forces to use captured German ammunition in their weapons, eliminating the need for repeated re-supply drops.{{Citation needed|date=January 2021}}

Overall the weapon failed in its intended role (to replace the Thompson) but proved effective in limited use in the hands of resistance forces.

==Users==
*{{flag|Republic of China (1912-1949)|name=Republic of China}}<ref name="mcnab2002">{{cite book |last=McNab |first=Chris|title=20th Century Military Uniforms |year=2002 |edition=2nd |publisher=Grange Books |location=Kent |isbn=1-84013-476-3|page=46}}</ref>
*{{China}}<ref name="mcnab2002"/>
*{{flagcountry|Czechoslovakia}}: 100 pieces from US supplies used by insurgent army and partisans during [[Slovak National Uprising]]
*{{flagcountry|France}}: Supplied to the [[French Forces of the Interior]].<ref>{{cite journal|journal=Firearms News|first1=Paul|last1=Scarlata|title=French World War II Small Arms: Part II|page=36|date=June 2017|issue=15}}</ref>
**[[Vichy France]]: Small number of captured examples issued to [[Milice française]]<ref>{{cite book|page=42|title=World War II Vichy French Security Troops|year=2018|isbn=978-1472827753|publisher=Osprey Publishing|first=Stephen M. |last=Cullen|series= Men-at-Arms 516}}</ref>
*{{flagcountry|Kingdom of Belgium}}: Supplied to the Belgian Resistance during WW2.
*{{flagcountry|Kingdom of Italy}}: Supplied to [[Italian resistance movement|Italian partisans]] during the Italian Campaign of WW2<ref>{{cite book|title=World War II Partisan Warfare in Italy|series= Elite 207 |first1= Pier Paolo |last1=Battistelli|first2= Piero|last2= Crociani|date=2015|publisher=Osprey Publishing|isbn=9781472808936|pages= 27, 36}}</ref>
*{{flagcountry|Netherlands}}: Supplied to the Dutch resistance during WW2.<ref name="mcnab2002"/>
*{{flagcountry|Philippines|1936}}: Used by the Philippine Army and Constabulary during the Post World War II era from 1945 to 1960s and used again by the local recognized guerrillas and irregular forces from 1942 to 1945 during World War II.{{citation needed|date=January 2019}}
*{{flagcountry|Poland}}: 152 pieces delivered in 1943 and 208 pieces delivered in 1944 to the [[Home Army]] by Allied aviation from North Africa and Italy{{citation needed|date=February 2024}}
*{{flagcountry|United States|1912}}<ref name="mcnab2002"/>
*{{flagicon image|Yugoslav Partisans flag (1942-1945).svg}} [[Yugoslav Partisans]]: Supplied by the OSS.<ref>{{cite magazine|title=Yugoslav Part II: World War II small arms: an assortment of small arms from friends and foe alike|first=Paul|last=Scarlata|magazine=Firearms News|date=1 October 2017|url=https://www.thefreelibrary.com/YUGOSLAV+PART+II%3A+WORLD+WAR+II+SMALL+ARMS%3A+AN+ASSORTMENT+OF+SMALL...-a0510936519}}</ref>

===Non-state groups===

* {{flagicon image|Flag of Ireland.svg|23px}} [[Provisional Irish Republican Army]]: Supplied to the IRA by [[Greek Cypriot]] group [[EOKA]].<ref>{{cite web |url=https://magill.ie/archive/rifles-ira |title = The Rifles of the IRA {{!}} Magill}}</ref>

==See also==
*[[List of individual weapons of the U.S. Armed Forces]]

==Bibliography==
*Nelson, Thomas B. (1963). ''The World's Submachine Guns, Volume I''. International Small Arms Publishers.
*Iannamico, Frank. (2004). ''United States Submachine Guns: From the American 180 to the ZX-7''. Moose Lake Publishing. {{ISBN|0-9742724-0-X}}.
*Brophy, William S. (1989). ''Marlin Firearms: A History of the Guns and the Company That Made Them''. Stackpole Books.

==References==
{{reflist}}

==External links==
*[https://web.archive.org/web/20060623233034/http://world.guns.ru/smg/smg67-e.htm Modern Firearms: United Defense UD M42 submachine gun]
*[http://ww2.rediscov.com/spring/VFPCGI.exe?IDCFile=/spring/DETAILS.IDC,SPECIFIC=10322,DATABASE=objects, Springfield Armory Collection: UD M42, 9MM]
*[http://ww2.rediscov.com/spring/VFPCGI.exe?IDCFile=/spring/DETAILS.IDC,SPECIFIC=10319,DATABASE=objects, Springfield Armory Collection: UD M42, .45 ACP]
*[https://patents.google.com/patent/US2289067 magazine patent]
*[https://patents.google.com/patent/US2342824 submachine gun patent]
*[http://www.americanrifleman.org/blogs/qa-M42-united-defense-submachine-gun American Rifleman article]
*[http://www.smallarmsoftheworld.com/display.article.cfm?idarticles=2162 Small Arms Review article]
*[https://elitadywersji.org/zrzuty/ website on Polish Home Army paratropers]

{{WWIIUSInfWeaponsNav}}

[[Category:Insurgency weapons]]
[[Category:World War II submachine guns]]
[[Category:Submachine guns of the United States]]
[[Category:World War II infantry weapons of the United States]]
[[Category:9mm Parabellum submachine guns]]
[[Category:Weapons of the Philippine Army]]
[[Category:Weapons and ammunition introduced in 1942]]