October 27, 2016:
A South Korean firm has developed a 127mm shell that is designed to automatically adapt to the type of ship it hits and penetrate far enough before detonating. Called APA (Armor Piercing Ammunition) this one is equipped to do maximum damage to key items kept deep inside a ship (like the engines, some electronics and the combat information center). Not a lot of details were released other than it is intended to function against targets as far as 24 kilometers distant.
The manufacturer (Poongsan) is also working on a GPS guided version, which is based on a 155mm GPS guided shell they are developing for the South Korean army. There is already a Swedish-American 155mm GPS guided shell which has been in service nearly a decade. GPS guided 127mm shells have been more difficult to make work.
An Italian firm has developed the Vulcano 127mm GPS guided shell that can hit targets over 100 kilometers away within 20 meters of its aiming point. This has not entered service yet. The U.S. Navy spent nearly a decade and over $600 million to develop a similar guided shell and failed. It is still uncertain if the Vulcano will affordable and reliable enough to find a market.
Problems with getting "smart shells" to work effectively are nothing new. Back in the 1980s, the American 155mm Copperhead round was developed, at great expense, to take out tanks with one shot. The Copperhead was laser guided. That is, it homed in on laser light that a forward observer was creating by pointing a laser at the target. It was the same technique used with laser guided bombs. But this was expensive technology for an artillery shell. Each of the 3,000 Copperhead shells eventually built cost several hundred thousand dollars (the price varied, up to half a million bucks, depending on who was doing the calculating). While a "dumb" artillery shell will land within 75 meters of the aiming point, the Copperhead would land within a meter or two. But so what? It turned out there were many easier, and cheaper, ways to destroy enemy tanks. This was demonstrated during the 1991 Gulf War, when a few Copperhead shells were used, successfully, but to reactions of, "whatever."
Russia developed its own version of Copperhead, Krasnopol, and sold some to India. During a 1999, war with Pakistan, high in the Himalayan Mountains, Krasnopol proved very useful in taking out enemy bunkers, without causing avalanches or destroying the few pathways up the steep hills. However, Krasnopol had not been tested at such high altitudes (over 4,000 meters) and in such cold weather. There were problems that had to be fixed. The Indians paid about $40,000 for each Krasnopol shell (two thirds what the Copperhead was supposed to cost originally) and eventually found it a good investment.
The eventual success of Krasnopol encouraged the American developers of the next generation smart shell, Excalibur. But GPS guided shells proved to be a tough technology to perfect, and when Excalibur arrived in 2007 it found itself with some stiff competition. In Iraq, the troops had been using the 227mm MLRS GPS guided rocket since 2005. With a range of 70 kilometers, a few GMLRS (G for "Guided") vehicles (each carrying six rockets) can cover a huge area with very accurate fire. The GMLRS has been a great success, and the army had to hustle to get enough rockets built to meet demand. The shorter range Excalibur was more popular because of its smaller explosive load. Each 45.5 kg (100 pounds) shell has about 9.1 kg (20 pounds) of explosives. The 227mm MLRS GPS rocket carried over 68 kg (150 pounds) of explosives. In too many cases range was the key factor. The GMLRS could reach the target, Excalibur could not. Now, Excalibur has a longer reach and will be called on more often. But Excalibur still has too much cheaper and more effective competition. More and more guided missiles are appearing, including some the infantry can carry with them. Excalibur is a major breakthrough for the past. A successful 127mm GPS shell for naval guns would also be a breakthrough but no one has managed to achieve it yet.
Meanwhile China, which purchased some Kransnopol shells has gone on and developed similar laser guided 155mm shells and some interesting variants. But all nations have found the GPS guided shell a more difficult design to perfect.