AGM-158 Joint Air-to-Surface Standoff Missile
After a development program with stops and starts, the AGM-158 Joint Air-to-Surface Standoff Missile (JASSM) entered production in 2009, and will be used by countries including the United States, Australia, the Netherlands and South Korea. It is a long-range (>250mi/370km) stealthy air-launched cruise missile. Its warhead is filled with the insensitive high explosive, AFX-757, and has hard target penetrator capability.
It will be the successor to the AGM-86 ALCM, which has longer range but is not stealthy. That missile's range is far longer with a lighter nuclear warhead, but still about double that of the JASSM with a conventional warhead. The ALCM, however, was intended to be launched outside the extremely strong air defenses of the Soviet Union, and it is unlikely that there will ever be a need to make an approach over as long as deep a border defense. Another missile, developed but never deployed, but with comparable range, was the air-launched version of the BGM-109 Tomahawk.
The project, which began in 1995, is the successor to the AGM-137 Tri-Service Standoff Missile, which was cancelled due to excessive costs. This model is the result of a competition with McDonnell Douglas (now part of Boeing), won by Lockheed Martin.
Production began in late 2001. It had problems during flight testing, leading to a hold on production in 2009. 
- Amy Butler (28 August 2009), "JASSM Production Gap Manageable, USAF Says", Aviation Week