M-4A1 Carbine SOPMOD 5.56mm

U.S. Army Lt. Colonel Daniel Christian (arm extended), 18th Airborne Corps, Military Transition Team (MITT), with U.S. and Iraqi Soldiers, Wasit Province, Iraq, 20 May 2005. LTC Christian is armed with a Special Operations Peculiar Modification (SOPMOD) M-4A1 Carbine.
U.S. Army Lt. Colonel Daniel Christian (arm extended), 18th Airborne Corps, Military Transition Team (MITT), with U.S. and Iraqi Soldiers, Wasit Province, Iraq, 20 May 2005. LTC Christian is armed with a Special Operations Peculiar Modification (SOPMOD) M-4A1 Carbine.

Today in WW II: 21 May 1942 Sinking of the Mexican tanker Faja de Oro by German submarine U-160, off Key West, precipitates Mexican declaration of war against Nazi Germany.   

M-4A1 Carbine 5.56mm Special-Operations Peculiar-Modified (SOPMOD)

US Army Sgt. John Maninga, 1st Bn., 187th Infantry Regiment, 3rd Brigade Combat Team, 101st Airborne Div., armed with a 5.56mm M-4 SOPMOD Carbine scans down Route Tampa, Bayji, Iraq, 10 December 2005.
US Army Sgt. John Maninga, 1st Bn., 187th Infantry Regiment, 3rd Brigade Combat Team, 101st Airborne Div., armed with a 5.56mm M-4 SOPMOD Carbine scans down Route Tampa, Bayji, Iraq, 10 December 2005.

The 5.56mm M-4 Carbine was enhanced to enable the individual Special Operations Forces (SOF) soldier to tailor the configuration of the weapon to the assigned mission and operational environment. When fitted with the Knight's Armament Corporation M4 Rail Accessory System (Picatinny type or MilSpec 1913), the M-4A1 Carbine becomes the M-4A1 Modular Weapon System (MWS). The SOF standardized accessories kit is known as the Special Operation Peculiar Modification (SOPMOD).

M-4A1 Carbine SOPMOD Components

SOPMOD M4A1 Accessory Kit
SOPMOD M4A1 Accessory Kit

The joint service M-4A1 SOPMOD program is managed by the Program Management Office at Naval Surface Warfare Center (NSWC) in Crane, IN. While the components of the SOPMOD M4 Accessory Kit (Block I) will change as technology and requirements shift, the chart above shows the range of options available to the warfighter as of April 2006.

The most important feature is the high degree of configurability so the soldier has standardized, versatile weapons accessories available to meet needs across SOF mission scenarios. These accessories increase operator survivability and lethality by enhanced weapon performance, target acquisition, signature suppression, and fire control.

SOPMOD Flash and Noise Suppressor

The SOPMOD Kit includes a suppressor and muzzle brake used to decrease M-4A1 Carbine flash and sound during firing without significantly changing the point of impact. The purpose of the suppressor is to increase the difficulty in locating the position from which the live fire occurred. The noise of firing is reduced by about 30 decibels.

The suppressor is designed to function wet and a little water (two to five cc's) will further reduce noise and first-round flash. Testing has shown that water in the suppressor does not interfere with the weapon, unless large quantities are present while the weapon is carried level or pointed up. The manufacturer recommends to add water from the rear just before installing the suppressor on the weapon. If the suppressor is already mounted, the weapon can be dipped into water then shaken out while pointed straight down.

Military Use of Sound Suppressors / Silencers is described on the linked page.

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