The Standard Missile – The US Navy’s Shield

USS Cowpens launches an SM-2 missile from a Mk41 VLS

The Ticonderoga class cruiser USS Cowpens launches a Standard SM-2 missile

To anyone who reads technothrillers the Standard missile will be familiar as the main armament of the US Navy’s AEGIS ships. Designed as an anti-aircraft missile, the 50-year-old missile programme has gradually expanded and taken on more roles as new requirements were identified and upgraded versions developed to suit. It’s now one of the most widely deployed naval missile systems in the world, with 15 countries currently using various versions.

The Standard programme goes back to 1963, when the US Navy started looking for a new SAM to replace several older versions that were in service at the time. To speed up development the body of the existing RIM-24 Tartar missile was used, but the new design had completely different electronics and a newly developed guidance package, making it far more effective and reliable than the RIM-24. Designated as the RIM-66 Standard it entered service in 1968; use of the RIM-24 body meant it could be easily retrofitted to ships that had carried the Tartar missile. More widely known as the SM1-MR (Standard Missile 1 – MediumRange) it was used during the Vietnam War and is still in service with several navies worldwide. The Standard uses a conventionally shaped missile body with four long, low-profile strakes for lift and stability and four guidance fins at the rear of the body. Guidance is semi-active radar homing (SARH,) meaning that the missile homes in on reflected energy from a guidance radar on the launching ship. The ship can control as many missiles as it has fire control radars.

The Standard missile's long range and ABM variants are fitted with additional boosters
The Standard missile’s long range and ABM variants are fitted with additional boosters

In the late 1970s, concerned at new Soviet developments in anti-ship missiles, the US Navy began working on a system to defend their aircraft carriers against mass missile attacks. The solution was the Ticonderoga-class cruisers. Fitted with the AEGIS system, based around the SPY-1 radar and an advanced battle management computer, these ships were designed to accurately track, designate and engage large numbers of missiles automatically. Their main weapon system was an advanced version of the Standard, designated the SM-2. Part of the upgrade was the addition of an inertial guidance system. This hugely expanded the number of targets the Standard system could attack. Before launch each missile was instructed to fly to a point near the target’s predicted location; in the last few seconds of its flight the target would be illuminated by a fire control radar, allowing the missile to guide itself in. This meant that an AEGIS cruiser could rapidly engage a large number of targets in sequence, because its APG-62 fire control radars could engage the first targets while missiles aimed at subsequent ones were automatically steering themselves to a fixed point. If targets changed course while the missiles were in flight the SPY-1 could send mid-course guidance updates so they would be in a viable attack position when the APG-62 illuminated their targets.

Early AEGIS cruisers launched RIM-66C or D model missiles from two twin-rail launchers which automatically reloaded from below-decks magazines. Later ships, and the Arleigh Burke-class destroyers that followed, used the Mk 41 Vertical Launch System (VLS.) The VLS allows a much higher rate of fire, which increases survivability against mass attacks. However the cells are too short to hold the RIM-67 SM-1ER and SM-2ER (ExtendedRange) missiles, which added a detachable booster rocket to the rear of the missile to increase range from 70 to 120km. The RIM-156, with a compact booster, was introduced in 1999 to solve this problem.

SM-2 Standard missile
Early Standard systems used single or double rail launchers. An SM-2 is fired from HMAS Sydney.

Originally designed to destroy aircraft and anti-chop missiles, the Standard has been modified to attack other types of targets. Early versions could be used against ships out to the radar horizon in SARH mode; later upgrades can attack beyond the horizon using inertial guidance with a terminal infrared seeker. Recent tests show that despite having a smaller warhead than the Harpoon anti-ship missile the Standard is more effective, especially against smaller ships, because it has more kinetic energy at impact. It’s also a lot more likely to get through modern anti-missile defences. Soviet, and later Russian, anti-ship missiles have been increasing in speed since the 1970s; the latest one is the SS-N-27 Sizzler, which cruises at subsonic speed then accelerates to Mach 2.9 to sprint through the target’s defences. By contrast the main western anti-ship missiles, the Harpoon and the French Exocet, attack at about Mach 0.8. This makes them highly vulnerable to modern close range weapons. By contrast the Standard flies at over Mach 3.

Currently the US Navy is supplementing its existing missile stocks with the new RIM-174 SM-6 version. This is a RIM-156 with the SARH seeker replaced by the active radar head from an AIM-120 AMRAAM; the use of active radar combined with the existing inertial guidance makes the missile more flexible and allows it to attack targets outside the line of sight of the launching ship’s fire control radars.

The most significant development of the Standard, however, is the RIM-161 SM-3. Now in service with the US Navy and Japan, the SM-3 was developed to intercept short and medium range ballistic missiles. By boosting the missile into the thinner upper atmosphere the SM-3 gets a hugely increased range; 700km in the Block I version and 2,500km in the Block II. Maximum height is 500km for Block I and 1,500km for Block II. The SM-3 uses GPS, inertial and SARH guidance to approach the target then carries out terminal homing with a long wave infrared seeker. The warhead contains no explosives; it destroys the inbound missile through kinetic energy at an impact speed of around Mach 4.

SM-3 missile
USS Lake Erie launches an SM-3 ABM interceptor

The SM-3 has performed well in tests, killing 16 out of 16 simulated ballistic missiles with 19 SM-3s expended. That’s a hit rate of over 84%. The upcoming Block IIA missile, due to enter service in 2015, will increase performance even more and allow the system to destroy some intercontinental ballistic missiles. In 2008 an SM-3 was used to destroy a satellite at an altitude of 247km. Although officially intended to destroy a malfunctioning satellite to reduce the hazard to other spacecraft, the launch was widely interpreted as a demonstration to China of the USA’s ASAT capability.

Because the USA hasn’t faced a credible air threat in decades the Standard hasn’t seen a lot of operational use, but when it has been fired it’s performed flawlessly. In 1988 USS Vincennes accidentally shot down an Iranian airliner with two SM-2MR missiles. This was a serious accident but the missile itself worked as intended. The same year an Iranian missile boat was destroyed by Standards in anti-ship mode.

It’s now half a century since development of the Standard began, but constant upgrades have maintained its capability and it’s now the leading naval anti-ballistic missile system as well as remaining highly capable against air and cruise missile targets. The US Navy plan to keep it in service until at least 2035 and possibly beyond. It’s likely that the Standard Missile will be the core of US naval air defence for a long time to come.