The U.S. Navy recently decided to develop an anti-ship version of its Tomahawk cruise missile, which was originally designed so ships could attack stationary targets deep inside enemy territory. In addition to the anti-ship upgrade current Tomahawks will be refurbished to extend their useful life from 15 to 30 years and new ones will continue being made so that Tomahawks can remain in service until 2040. By then it will be replaced by the NGLAW (Next Generation Land Attack Weapon).
Development of a successor to the Tomahawk has been underway since the 1990s and the current (NGLAW) concept is for a cruise missile that will be heavier (2.2 tons), have a longer range (2,000 kilometers), and a larger (one ton) warhead than the Tomahawk. The NGLAW will be stealthier and use a combination of new guidance and targeting systems to improve the chances of success. Price will probably be the key factor but it is expected to cost at least twice as much as the current Tomahawk. The Tomahawk, when it showed up in the 1980s, was one of the first UAVs, it just wasn't reusable. But UAVs that carry bombs and missiles and can be reused are going to provide competition for NGLAW
Since the 1990s Tomahawk has received more and more upgrades and new capabilities. The more recent ones led to the anti-ship capability as well as overall improvements in the guidance system and defensive capabilities against electronic jamming. The need for these new features was seen in 2015 when the navy tested the current Block 4 Tomahawk to see ifs its new two way communications capability could enable it to effectively hit moving targets. The Block 4 managed to do so, but not under combat conditions. That is, not with warships using defensive or electronic weapons to shoot down the incoming missile or mislead its guidance system. The recent navy test used a nearby aircraft (which could be a UAV) that was tracking the exact location of the target ship. That could also be done from a space satellite. Thus a fully developed anti-ship capability for Tomahawk will require upgrades in the guidance system to make it capable of operating without constant two-way communications.
The navy is aware of the fact that Tomahawk is not the ideal anti-ship missile. Against modern defenses anti-ship missiles have to move faster than a Tomahawk and be equipped with a better terminal guidance system. The speed problem cannot be fixed, but the Tomahawk could be equipped with a more capable terminal guidance system. That might be able to handle the tracking and targeting systems for gun and missile systems designed to knock down anti-ship missiles when they get close. In any event, Tomahawk Block 4 has a way to go before it is a competitive anti-ship missiles against modern warships. But developing and testing upgrades will give Tomahawk a useful anti-ship capability, just not make it the most effective anti-ship missile out there.
There are apparently some novel concepts for using a radically new anti-ship warhead that turns Tomahawk into a two stage missile with the warhead making the final attack at much higher speed. That may not work but because Tomahawk is a stable and reliable design with lots of combat experience it is easier to tinker with the guidance system, warhead and range and come up with affordable new capabilities that work. That works because one reason for the continued usefulness of Tomahawk is its ability to do more and more things reliably.
Because of these constant improvements and consistent reliability American (and other) warships continue to use Tomahawks in combat on a regular bases. The targets tend to be on land and not mobile. Most of these uses are publicized, but some are not. Several hundred Tomahawks were used against Libya in 2011 and that demonstrated the effectiveness of Tomahawks in delivering major airstrikes on short notice, anywhere in the world without losing more expensive manned aircraft and exposing their pilots to getting shot down and captured.
The Tomahawk was introduced in 1983 and over 6,000 have been manufactured so far. The U.S. Navy has fired over 2,200 in combat and over 600 for training and testing. The U.S. Navy currently has over 3,000 Tomahawks on its warships or in storage.
The current Tomahawk, the RGM-109E Block 4 Surface Ship Vertical Launched Tomahawk Land Attack Missile weighs 1.2 tons, is six meters (18 feet) long, has a range of 1,600 kilometers, getting there at a speed of 600-900 kilometers an hour, flying at an altitude of 17-32 meters (50-100 feet), and propelled by a jet engine generating only 600 pounds of thrust. Accuracy is on a par with JDAM (10 meters/31 feet). The Block 4 Tomahawk can be reprogrammed in flight to hit another target and carries a vidcam to allow a missile to check on prospective targets.
In 2012 the Block 4s were recently upgraded so that they can hit moving targets. This was for making Tomahawk capable of carrying out some anti-ship missions, although it can also hit moving land targets. The Tomahawk has been a primary land attack weapon for surface ships and submarines since the 1990s. The Block 3 entered service in 1994, but the Block 4 was a big upgrade with the addition of GPS and remote control in flight.