The U.S. Army is once more upgrading its MGM140 ATACMS (Army Tactical Missile Systems) artillery rockets. The ATACMS is a 610mm ballistic missile that fits in the same size container that normally holds six 227mm MLRS rockets. The new upgrade is because it was realized that ATACMS has sufficient range to reach ships far offshore and that the U.S. pioneered the development of terminal guidance systems ballistic missiles in the 1970s (the Pershing mobile missile). Since then the U.S. has developed similar guidance systems so that high-speed missiles can hit moving targets. So it is not a difficult feat to develop a terminal guidance system for ATACMS that searches for a certain size ship and heads for it while moving at more than a thousand meters a second (faster than a very speedy bullet).
Most current ATACMS are armed with a 227 kg (500 pound) high explosive warhead. The U.S. used over 700 ATACMS in Iraq and Afghanistan and was satisfied with their performance. Nearly 4,000 ATACMS have been built since the mid-1980s and about 70 percent are still available for another upgrade. ATACMS currently use GPS guidance to hit targets up to 300 kilometers away. This makes ATACMS sort of like the popular 500 pound JDAM smart bomb used by the air force but not requiring an aircraft to deliver it.
All the new ATACMS needs is the GPS coordinates of the moving target (which can be on land or sea). Since max flight time (at max range) is only a few minutes it is easy to predict where the moving target will be based on aerial, satellite or sonar detection. It takes less than a minute to update the guidance system and launch. If nothing else this will give potential naval foes something more to worry about and be a popular export items as well.
When the U.S. Army first introduced ATACMS in the late 1980s it designed fancy warheads that distributed lots of smaller bomblets. While these worked, there was always a problem with some of the bomblets not self-destructing and later going off when civilians, or American troops, came along. Not a popular weapon. Then, when a version with GPS guidance and a single 500 pound high explosive (or "unitary") warhead was introduced, it proved very popular. These rockets cost about $1.2 million dollars each. A 500 pound JDAM costs about $40,000, although you can add a few thousand dollars more to cover the expense of operating the jet bomber that delivered it.
Another advantage of ATACMS is the ability to quickly move it and its launcher by air to anywhere in the world. This is because of HIMARS. Only costing about $3 million each, these smaller, truck mounted MLRS (HIMARS) rocket launcher systems carries only one, six rocket (or one ATACMS) container (instead of two in the original MLRS vehicle). But the 12 ton truck can fit into a C-130 transport (unlike the 22 ton tracked MLRS) and is much cheaper to operate. The first HIMARS entered service in 2005, about a year after GPS guided rockets did. HIMARS proved more effective and popular than expected.
The army is already developing a new, smaller, longer ranged ATACMS that will enable two in a container that currently holds one. But this new ATACMS won’t be available until the mid-2020s.