If everything goes according to plan, an upgrade for the M4A1 in use  the US Special Operations Forces will make them more stealthy as it involves the use of integrated suppressors for their weapon. Last 27 July SIG Sauer was awarded a contract for the M4A1 Suppressed Upper Receiver Groups (SURG) as announced by Defense.gov:

Sig Sauer Inc., Newington, New Hampshire, was awarded a $48,000,000 five-year, indefinite-delivery/indefinite-quantity, firm-fixed-price contract for the acquisition of the Suppressed Upper Receiver Group (SURG).  The SURG weapon is an upgrade of the M4A1 lower receiver group in support of U.S. Special Operations Command (USSOCOM) Procurement Division.  Fiscal 2018 procurement funds in the amount of $24,620 are being obligated at the time of award.  The majority of the work will be performed in Newington, New Hampshire, and is expected to be completed by July 2023.  This contract was awarded through full and open competition.  USSOCOM headquarters, MacDill Air Force Base, Florida, is the contracting activity (H92430-18-D-0005).

Previously, SIG Sauer won a contract for the MCX Rattler PDW for close quarters combat for use by the USSOCOM.  Whilst the MCX Rattler PDW uses the .300 Blackout round, it can be readily converted to fire the 5.56mm round.

The SURG program was first identified in 2015 but was abandoned in 2016 and was later restarted. The requirements of the USSOCOM are a 5.56 NATO upper receiver group with an integrated suppressor rather than having a separate suppressor. According to Soldier Systems, which also revealed a photo giving us a first look of the SURG, it should be able use M855A1 and the MK318 MOD0 / MOD1 cartridges and be able to fire at least 1,200 rounds without lubrication.

First Look: SURG mounted to a regular M4 lower (Source: Soldier Systems)

Further information from Soldier Systems indicate a requirement for a more compact SURG, preferring  a full length of 21 inches but could go not more than 25.5 inches with the barrel being 11.5 inches in length. Ideal weight is 4.5lbs but not more than 7lbs. Color should be Coyote 498.

One thing which I think is a very much thoughtful add-on to the requirements apart from the all important sound suppression, is that the SURG should be able to prevent sustained burns due to contact between the suppressor and operator through 1 layer of clothing. Cans go hot due to sustained firing and preventing burns is one thing that is to be considered when designing the front end of a weapon.

The U.S. Marines and the Army are also looking into expanded use suppressors realizing the benefits of investing in suppressors such as minimize hearing loss and long term hearing damage apart from the tactical benefits in terms of better communications, muzzle flash suppression and lower sound signature makes them harder to spot.

Top photo: U.S. Soldier from 1st Battalion, 10th Special Forces Group (Airborne) with suppressed M4 in Germany (Source: DVIDSHub.net)