A Marine Corps battery (six guns) of M777 155mm howitzers was sent to Syria in early 2017 to support the SDF Kurdish militia as it advanced towards and took the ISIL (Islamic State in Iraq and the Levant) capital of Raqqa. The marines fired mostly M1156 GPS guided shells and did so at extreme ranges. In doing so they wore out the barrels on two of their howitzers. Normally the M777 barrel can fire up to 2,500 shells before wearing out but barrel life depends on what type of shell your fire. If you fire the longer range shells (which the marines did) barrel life is much reduced (to about a thousand rounds). While the GPS guided shells reduced the need for firing a lot of shells, the Americans also noted that fewer howitzers were required to provide accurate artillery support and even in Afghanistan some isolated artillery units (usually a battery or just a section of two guns) fired a lot of GPS guided shells and provided timely and accurate fire often at extreme range.
To deal with this problem a new full-bore chrome-lined barrel was developed. This more expensive barrel lasts about 50 percent longer than current howitzer barrels. The marines were only scheduled to get about a hundred of the new chrome lined barrels but the Department of Defense is re-thinking that because the marine M777s most frequently end up in situations as occurred in Syria. The marines were to receive their first chrome lined barrels in 2019 but that may happen sooner.
All this is the price of progress. In 2007 the U.S. Army and Marine Corps received their first M777A1 lightweight 155mm howitzers. The M777s cost $1.9 million each and the U.S. has bought about a thousand of them so far, for use by the army and marines (who received nearly 400 of them). The manufacturer, BAE, has also received a contract to refurbish dozens of M777s that returned from service in Afghanistan. This cost $91,000 per howitzer. The British designed howitzer is also used by Canada and Britain. The army uses M777s in airborne and Stryker brigades while for the marines all their field artillery is towed. A five ton truck is used to tow the guns, but a special, 4.5 ton LWPM (Lightweight Prime Mover) is available to do that as well.
The M777 is a British design and, at four tons, is the lightest 155mm towed howitzer ever fielded. A crew of five fires regular rounds to 24 kilometers and RAP (rocket assisted projectiles) rounds to 40 kilometers. M777 Fire control is handled by computerized system that allows faster response time and more accurate shooting. Users have found the M777 accurate and reliable.