A collective term which refers to a group of multi-purpose (though primarily air defense) guided missiles used by several navies throughout the world, most notably the USA, Canada, Australia and Japan. There are a confusingly large number of variants of this missile system, and a number of revisions of each variant. Consequently, keeping them all straight is something of an interesting task.
All Standard missiles have several common features. First, they all employ semi-active radar homing, though some of the newer variants have secondary modes. Second, they all employ various sorts of blast-fragmentation warheads. The earliest versions were continuous-rod, and later versions are blast-frag or directed blast-frag. All Standard missiles, save the SM3, employ a dual-mode proximity fuze with a secondary contact detonator. In anti-surface mode, the proximity fuze is disabled. They also all share a common main airframe.
The first of the series is the RIM-66 Standard Missile, nowadays known as SM1-MR (Standard Missile 1, Medium Range). This replaced the older Tartar missile system as the USN's primary air defense missile. It used a slightly modified version of the Tartar airframe, with four stabilizer strakes and a cruciform tail which served as the control surface. This same airframe form has been used for all Standards since then. Propulsion is in the form of a solid-fuel rocket motor, allowing a maximum speed of about Mach 2.5. It has a maxiumum range of 15 to 20 nautical miles, which was significant at the time it was introduced, but is considered a bit lacking nowadays. Also, like its predecessor, SM1-MR has a surface attack mode, though this is largely an afterthought. One of the major problems the SM1 has, is that it requires the target to be illuminated by fire control radar all the way from launch to impact. This means that the target has lots of warning and time to evade, and further, that a ship can engage no more targets than it has fire control designators. This missile was used aboard the Adams-class destroyers and several other platforms, and most recently the Perry-class frigates. As of 2006, it has been withdrawn from USN service.
The RIM-67 SM1-ER is a slight modification of the SM1-MR missile which added a large rocket booster that extended the range to nearly 100 nmi. This may have increased the speed as well, though the actual maximum speed is still classified. It was used on Leahy, Belknap and Farragut-class warships, though it was replaced by the SM2-ER on the Leahys and Belknaps shortly before their retirement from service. Other than extended range, this weapon offers little improvement over the SM1-MR. It was withdrawn from service in the late 1980s.
The SM2-MR (Standard Missile 2, Medium Range) is almost an entirely new missile internally, despite sharing SM1's airframe. Paradoxically, it also carries the RIM-66 designation. Because of this, the weapon is almost universally referred to as SM2 vice RIM-66 in Naval usage. It employs a new, more powerful rocket motor for better acceleration, range and top speed and has a more accurate and capable seeker. In particular, the new SM2 seeker does not require illumination except for the last few seconds of flight. This means that the enemy has much less warning and time to evade. The warhead is also increased from 90 pounds to 137. It is significantly more resistant to jamming and decoys, and has better fin motors for improved maneuverability. Its range has been extended to 45 to 75 nmi. More attention was also paid to its surface-attack mode. Since the initial deployment of this weapon, several more sub-variants, known as Blocks, of this missile have been developed.
The most recent is Block IIIb, which includes thrust vectoring, plus an intertial guidance unit and a secondary infrared seeker. This overcomes issues with the earlier missiles where the launching ship's illuminators could be saturated by too many targets, or worse yet destroyed. With Block IIIb, the missile is launched to a set of coordinates which corresponds to the enemy's projected location. These coordinates are updated by the launching ship during flight. When the missile nears its target, one of two things happens - either the warship illuminates the target with radar and the SM2 homes in on this, or it locks onto the target's heat signature (infrared guidance) and guides itself the rest of the way in. This has several important implications. One, destroying or jamming a ship's illuminators (or forcing it to shut them down) does not remove their missile capability. Two, the missile can now act in a nearly fire-and-forget manner, making 'panic launches' wherein the ship dumps its entire missile magazine at an incoming flight of enemy aircraft or missiles, actually useful. Thirdly, this enables the SM2 Block IIIb to engage targets over the radar horizon, such as ships or low-flying cruise missiles. Finally, this renders the missile nearly invulnerable to single-mode decoys, such as chaff or flares. Its thrust-vectoring capability also gives a marked increase in maneuverability, placing it in the same league as the notoriously maneuverable Aster missile series. Its top speed is improved as well, though the exact speed is classified.
SM2-ER, still designated RIM-67, was the long-range version of the early-block SM2-MR. It was deployed aboard the Leahy and Belknap-class cruisers and Kidd-class destroyers. The only nation still using it is Taiwan, though the newer variants use the Block IIIb SM2 as their second stage. They have a very long range, nearly 190 nmi, but the length of the rocket booster precludes their use in the Mk. 41 VLS. Because of this, they were withdrawn from USN service in the late 1990s when the last Kidd-class destroyer decommissioned and transferred to Taiwan.
SM2 block IVA is technically a variant of the SM2-MR (RIM-66), but is sometimes referred to at the SM2 Block IVA ER, and has a new designation, RIM-156. It is essentially an SM2 Block IIIb with a short but exceedingly powerful booster attached. It just barely fits inside a full-depth VLS cell. The booster extends its range to approximately 150 nmi. This, combined with higher acceleration and the improved guidance system from the Block IIIb, allows it to be used not only as an anti-aircraft and anti-cruise-missile weapon, but allows it to engage theater ballistic missiles. This is the current weapon employed for the Navy's TBMD system. Finally, its very long range allows it to be used as an over-the-horizon anti-ship missile, nearly replacing Harpoon on the Ticonderoga-class, and supplanting it entirely on the Arleigh Burke-class. Though it packs a much smaller warhead than Harpoon (137 lb versus 482 lb) it arrives with much more kinetic energy, allowing it to penetrate into critical parts of the ship before exploding. This also means that a direct hit will obliterate most aircraft, even large ones like the Tu-22M Backfire. Due to its great expense, and reduced maneuverability at short range, the Block IVA has not replaced the Block IIIb entirely.
The third variant, currently in low-rate production, is the RIM-161 SM3. This is a long-range, ultra-high-speed missile, based on the SM2 Block IVA. It is intended for intercepting ballistic missiles, though it has some capability against cruise missiles and fixed-wing aircraft as well. It has a range of 200 nmi or greater, and a hit-to-kill kinetic (non-explosive) penetrator warhead. This makes it unsuitable for anti-surface warfare, but ideal for destroying IRBMs.
SM4 (RGM-156) was the cancelled, though nominally successful, Land Attack Standard, designed for engaging hardened land targets. The project was cancelled due to cost overruns. Though the USN is mum on the matter, it is suspected that the INS of SM2 Block IIIb and Block IVA nearly duplicates this capability anyway.
Also in the pipeline is the SM6 (the SM5 designation seems to be earmarked for something else). This is essentially an SM2 Block IVA with an improved rocket motor and the active-radar seeker from the AIM-120 AMRAAM. It would also retain the IR and SARH modes, for use in high-jamming environments. Little else is known about this missile.