Thanks to Iranian and North Korean ballistic missiles, the U.S. Navy is now scrambling for a way to enable its warships to reload their missile launch tubes at sea. For over two decades, this was not seen as a priority. But with the widespread use of the Aegis anti-missile system on ships, and the prospect of having to shoot down a lot of hostile ballistic missiles, while also fending off hostile aircraft, the need for reloading VLS cells at sea is now, well, important.
Over the last three decades, the United States, and later several other nations, have adopted the eight cell VLS (Vertical Launch System), where anti-aircraft, anti-ship or cruise missiles are launched directly from the vertical launch tubes (cells) just beneath the decks of warships. The launch tubes also contain electronic connections that enable the crew to monitor the condition and readiness of the missiles. Most cells contain only one missile, although the smaller Sea Sparrow anti-aircraft missile can fit four to a VLS cell. Since 1982, over 11,000 VLS cells have been installed in nearly 200 American and foreign warships. The most common VLS user is the American Burke class destroyer, with 90 VLS cells. A smaller number of cruisers have 122 VLS cells each. Some of the older Spruance class destroyers got 61 VLS cells.
In the 1980s, there was some debate over the need for an at-sea reloading capability. A system was developed, but it meant losing six cells (three for the forward VLS cells, and three for the ones aft, in the rear of the ship). This crane system was dropped, so that the ships could use more cells for missiles. Back then, it was believed that any future war would mainly be a series of hard fought initial battles, when every VLS cell counted. But with ballistic missile defense, an Aegis ship might only be carrying 20-30 Aegis guided anti-missile missiles (the rest being anti-aircraft), and you might not want to send that ship all the way back to a base that could reload the VLS tubes.
At the moment, Aegis anti-missile systems are hot. The U.S. government, encouraged by the high success rate (83 percent) of Aegis SM-3 missiles to shooting down ballistic missiles, has been expanding the number of SM-3 equipped ships. With 18 Aegis anti-missile equipped ships in service now, and plans to have more than twice as many in the next few years.
Converting Aegis ships to fire anti-missile missiles costs about $12 million a ship, mainly for new software and a few new hardware items. This is seen as a safe investment. To knock down ballistic missiles, an Aegis equipped ship uses two similar models of the U.S. Navy Standard anti-aircraft missile, in addition to a modified version of the Aegis radar system, tweaked to also track incoming ballistic missiles.
Now the government wants to use Aegis more aggressively to block Iranian or North Korean ballistic missiles. This means buying over a thousand SM-3 missiles. These currently cost about $10 million each, and the next upgrade (which will deliver more accuracy and reliability) will raise that to $15 million each. While the expanded Aegis program will cost about $20 billion, it's seen as the cheapest way to provide reliable anti-missile defense against Iran and North Korea.
The basic anti-missile missile RIM-161A, also known as the Standard Missile 3 (or SM-3). It has a range of over 500 kilometers and max altitude of over 160 kilometers. The Standard 3 is based on the anti-missile version of the Standard 2 (SM-2 Block IV). This SM-2 missile turned out to be effective against ballistic missile warheads that are closer to their target. One test saw a SM-2 Block IV missile destroy a warhead that was only 19 kilometers up. An SM-3 missile can destroy a warhead that is more than 200 kilometers up. But the SM-3 is only good for anti-missile work, while the SM-2 Block IV can be used against both ballistic missiles and aircraft. The SM-2 Block IV also costs less than half what an SM-3 costs.
The SM-3 has four stages. The first two boost the interceptor out of the atmosphere. The third stage fires twice to boost the interceptor farther beyond the earth's atmosphere. Prior to each motor firing it takes a GPS reading to correct course for approaching the target. The fourth stage is the 20 pound LEAP kill vehicle, which uses infrared sensors to close on the target and ram it. The Aegis system was designed to operate aboard warships (cruisers and destroyers that have been equipped with the special software that enables the AEGIS radar system to detect and track incoming ballistic missiles). However, there is also a land based version that Israel is interested in buying.