RIM-7 Sea Sparrow is a US ship-borne short-range anti-aircraft and anti-missile weapon system,
primarily intended for defense against anti-ship missiles. The system was developed in the
early 1960s from the AIM-7 Sparrow air-to-air missile as a lightweight "point defense" weapon
that could be retrofitted to existing ships as quickly as possible, often in place of
existing gun-based anti-aircraft weapons. In this incarnation it was a very simple system,
guided by a manually aimed radar illuminator. Since its introduction, the Sea Sparrow has
undergone significant development and now resembles the AIM-7 only in general form;
it is larger, faster and includes a new seeker and a launch system suitable for vertical
launch from modern warships. Fifty years after its development, the Sea Sparrow remains an
important part of a layered air defense system, providing a short/medium-range component especially
useful against sea-skimming missiles.
History Background
High-speed jet aircraft flying at low altitudes presented a serious threat to naval forces
in the late 1950s. Approaching under the local horizon of the ships, the aircraft would suddenly
appear at relatively close ranges, giving the ships only seconds to respond before the
aircraft dropped their payloads and withdrew. This gave the aircraft an enormous advantage
over earlier weapons such as dive bombers or torpedo bombers, whose low speed allowed
them to be attacked with some effectiveness by anti-aircraft guns. The advantage was so
great that when the Royal Navy was faced by the threat of the new Soviet Sverdlov class
cruiser, they responded in a non-linear fashion by introducing the Blackburn Buccaneer aircraft
to attack them. Further improving the capabilities of aircraft
against ships were a variety of precision-guided weapons. Early designs were first used in
World War II with manually controlled weapons such as the Fritz X, and evolving into semi-autonomous
cruise missiles, such as the Raduga KS-1 Komet, that relied on a combination of initial guidance
from the launching aircraft and terminal guidance on the missile itself. These systems allowed
the aircraft to launch their attacks from outside the range of shipboard anti-aircraft
weapons, in relative safety. Only the presence of defensive fighters operating at long ranges
from the ships could provide cover against these attacks, by attacking the launch aircraft
before they could close on the ships. US Navy doctrine stressed long-range air cover
to counter both high-speed aircraft and missiles, and development of newer short range defenses
had been largely ignored. While developing expensive long-range fighters like the Douglas
F6D Missileer, most ships were left equipped with older weapons, typically Bofors 40 mm
guns or Oerlikon 20 mm cannons. By the early 1960s their capability against modern aircraft
and missiles was limited; a lack of fast-reacting mounts, gunsight radars of limited accuracy,
and long settling times for the fire control systems all meant that the guns were unlikely
to be able to respond effectively against high-speed aircraft.
The introduction of sea-skimming missiles dramatically increased the threat against
these ships. Unlike the earlier generation of anti-ship missiles, sea-skimmers approached
at low level, like an attack aircraft, hiding themselves until the last moment. The missiles
were relatively small and much harder to hit than an attacking aircraft. While the older
defences might be considered a credible threat to a large aircraft at low altitude or a missile
approaching at higher altitudes, against a sea-skimming missile they were useless. To
successfully counter this threat, ships needed new weapons able to attack these targets as
soon as they appeared, accurately enough to give them a high first-attempt kill probability
- there would be little time for a second attempt.
Point defence missile system The US Army faced a similar problem defending
against attacks by high-speed jet-powered attack aircraft. In this case the local horizon
was generally even more limited, blocked by trees and hills, and engagement times could
be measured in seconds. They concluded that a gun-based system was simply unusable in
this role; by the time the radar had locked-on and the gunsight calculated proper "lead"
there would be no time to shoot at the target while it was within a gun's relatively short
range. Missiles, on the other hand, could progressively tune their approach while they
were flying toward the target, and their proximity fuses meant they only needed to get "close
enough". In 1959 the Army started development of the
MIM-46 Mauler, which mounted a new high-speed missile on top of the ubiquitous M113 Armored
Personnel Carrier chassis, along with a medium-range search radar and a separate tracking and illumination
radar. In order to deal with the quick response times needed, the fire control system was
semi-automatic; operators would view targets on the search radar and prioritize them, the
fire control system would select ones within attack range and automatically slew the missiles
toward them and launch. Since the missile would be operating close to the ground in
highly cluttered environments, it used a combination of beam riding along the illumination radar
and an infrared seeker in the nose, which allowed tracking as long as either the path
in front or in rear of the missile remained free of obstructions.
These same basic engagement parameters - high-speed and the associated fleeting sighting times
- applied to sea-skimming aircraft and missiles as well. The Navy intended to adapt the Mauler
to shipboard use by removing its search radar and wiring it into the existing ship-borne
radar systems instead. The 9-box launcher and illuminator radar would be retained in
a relatively compact mount. Development started in 1960 under the "Point Defense Missile System",
the naval version to be known as the "RIM-46A Sea Mauler". The Navy was so confident in
the Sea Mauler that they modified the design of their latest frigates, the Knox class,
to incorporate a space on the rear deck for the Sea Mauler launcher.
The Navy's confidence in Mauler proved misplaced; by 1963 the program had been downgraded to
a pure technology development effort due to continued problems, and was canceled outright
in 1965. All three of the stakeholders, the US Army, US Navy and British Army, started
looking for a replacement. While the British took a longer-term approach and developed
the new Rapier missile, the US Army and Navy scrambled to find a system that could be deployed
as quickly as possible. Facing the problem of guidance in a cluttered environment, the
Army decided to adapt the infrared AIM-9 Sidewinder missile into the MIM-72 Chaparral. This was
based on the AIM-9D, a tail-chaser, and would be useless for the Navy where its targets
would be approaching head on. They required a radar-guided system, and this naturally
led to the AIM-7 Sparrow. They also considered Chaparral for smaller ships due to its much
smaller size, but no such fits were ever attempted. Basic point defence missile system
Quickly organizing the "Basic Point Defense Missile System", BPDMS, the then-current AIM-7E
from the F-4 Phantom was adapted to shipboard use with surprising speed. The main developments
were the new Mark 25 trainable launcher developed from the ASROC launcher, and the Mark 115
manually aimed radar illuminator that looked like two large searchlights. Operation was
extremely simple; the operator would be cued to targets via voice commands from the search
radar operators, and he then slewed the illuminator onto the target. The relatively wide beam
of the radar only needed to be in the general direction of the target, the continuous wave
signal being Doppler shifted by the moving target and showing up strongly even if it
was not centered in the beam. The launcher would automatically follow the motions of
the illuminator, so that when the missile was fired it would immediately see the signal
being reflected off the target. In this form the Sea Sparrow was tested on
the USS Bradley starting in February 1967, but this installation was removed when the
Bradley was sent to Vietnam later that year. Testing continued, and between 1971 and 1975
Sea Sparrow was fitted to 31 ships, DE-1052 to 1069 and DE-1071 to 1083. The "missing
ship" in the series, USS Downes was instead used to test an upgraded version.
The Sea Sparrow was far from an ideal weapon. Its rocket engine was designed with the assumption
that it would be launched at high speed from an aircraft, and therefore is optimized for
a long cruise at relatively low power. In the surface-to-air role one would rather have
very high acceleration in order to allow it to intercept sea-skimming targets as soon
as possible. The power profile is also suitable for cruising in thin air at high altitudes,
but at low altitudes it does not produce enough power to overcome drag and dramatically decreases
range; some estimates indicate that the Sea Sparrow may be effective only to 10 kilometres,
about one quarter of the range of the air-launched Sparrow. An engine of much higher power would
greatly improve performance, in spite of a shorter burning time.
Another problem is that the Sparrow is steered with its mid-mounted maneuvering wings. These
were used on the Sparrow because they required less energy for basic maneuvers during cruise,
but this made the missile less maneuverable overall, which was not well suited to the
quick-reaction weapon. Additionally, the powered wings meant that they could not easily be
adapted to fold, and therefore the launcher cells were sized to the wings instead of the
missile body, taking up much more room than required. Although the Sea Sparrow was meant
as a small missile system that could be fit to a wide variety of ships, the launcher was
relatively large and was deployed only to larger frigates, destroyers and aircraft carriers.
Finally, the manually aimed illuminator was of limited use at night or in bad weather,
which was hardly encouraging for a ship-borne weapon where fog was a common occurrence.
Improved basic point defense missile system
In 1968, Denmark, Italy, and Norway signed an agreement with the US Navy to use the Sea
Sparrow on their ships, and collaborate on improved versions. Over the next few years
a number of other countries joined the NATO SEASPARROW Project Office, and today it includes
12 member nations. Under this umbrella group, the "Improved Basic Point Defense Missile
System" program started even while the original version was being deployed.
IBPDMS emerged as the RIM-7H, which was essentially the RIM-7A with the mid-mounted wings modified
to be able to fold. This was done in a fashion similar to carrier-based aircraft; the wings
were hinged at a point about 50% along the span, with the outer portions rotated back
toward the body of the missile. This allowed them to be stored in tighter container tubes
in the new Mark 29 launcher, and flip open automatically when they were released from
the tube. The seeker was modified to work with a variety
of guidance radars, including those being used with existing European missile systems.
Production of the RIM-7H began in 1973 as NATO Sea Sparrow Missile System Block I. For
the US Navy's use the new MK-95 illuminator system was also introduced, similar to the
original Mark 115 but with automatic guidance that could be used in any weather. The MK-95
formed the basis of the highly automated Mark 91 fire control system.
Missile upgrades In 1972 Raytheon started a Sparrow upgrade
program to arm the upcoming F-15 Eagle, producing the AIM-7F. The F model replaced the older
analog guidance system with a solid state version that could operate with the F-15's
new pulse-doppler radar. The guidance system was much smaller, which allowed the warhead
to be moved from its former rear-mounted position to one in front of the mid-mounted wings,
and increased in weight to 86 lbs. Moving it forward also allowed the rocket engine
to be enlarged, so it was replaced by a new dual-thrust engine that quickly accelerated
the missile to higher speeds, and then settled to a lower thrust for cruise. The new missiles
were quickly adapted for the naval role in a fashion similar to the RIM-7H, producing
the RIM-7F. The new missile used the lower model designation in spite of the newer technology
than the H model. Another major upgrade to the AIM-7 followed,
the AIM-7M. The M included a new monopulse radar seeker that allowed it to be shot downward
from a higher-altitude aircraft at a target otherwise masked by the ground. The new model
also included a completely computerized guidance system that could be updated in the field,
as well as further reducing weight for yet another warhead upgrade. The computerized
guidance system also included a simple autopilot that allowed the missile to continue flying
toward the last known target location even with the loss of a signal, allowing the launch
platform to break lock for short periods while the missile was in flight. All of these modifications
also improved performance against low-altitude sea-skimming targets as well. The M model
entered US operational service in 1983. The original RIM-7E was capable to fly at
about mach 2+, between 30 and 15,000 meters, with a range of 15-22 km. The RIM-7F enhanced
the performances, but also the proximity fuse vs low flying targets, as the minimum altitude
was reduced to 15 meters or less. The RIM-7M was capable to strike down to 8 meters, so
it was somewhat quite capable vs missiles such the Exocet.
While the M model was being worked on, the US Navy also introduced an upgrade for the
Mark 91 fire control system, the "Mark 23 Target Acquisition System". TAS included a
medium-range 2D radar and IFF system that fed information to a new console in the ship's
combat information center. The Mark 23 automatically detected, prioritized and displayed potential
targets, greatly improving reaction times of the system as a whole. The Mark 23 is also
used to select targets for most other weapons systems, including gunfire and other missile
systems. TAS started entering the fleet in 1980.
The NSPO also used the M series upgrade as an opportunity to upgrade the system to allow
it to be launched from a Vertical Launching System. This modification uses the "Jet Vane
Control" package that is added to the bottom of the missile. On launch, a small engine
in the JVC boosts the missile up above the launching ship, then uses vanes positioned
in its own exhaust to quickly slew the missile into the proper alignment with the target,
which is fed to the JVC during launch. As far as the Sea Sparrow is concerned, there
is no difference between being launched directly from a trainable launcher or using JVC, in
both cases the missile becomes active looking directly at the target.
A final upgrade to the Sparrow was the AIM-7P, which replaced the M's guidance system with
an improved model that allowed mid-course upgrades to be sent from the launching platform
via new rear-mounted antennas. For air-to-air use this allowed the missile to be "lofted"
above the target and then be directed down towards it as it approached; this gives the
missile greater range as it spends more time in thinner high-altitude air. This meant that
the new version could also be directly guided against surface targets that would otherwise
not show up well on radar, allowing the ship's more powerful search radars to provide guidance
until the missile approached the target and the reflected signal grew stronger. This also
gave the Sea Sparrow a very useful secondary anti-shipping role that allows it to attack
smaller boats. On 1 October 1992 during NATO exercises in
the Aegean Sea the USS Saratoga accidentally launched two Sea Sparrow missiles. These hit
the Turkish destroyer TCG Muavenet in the bridge and CIC, killing five of the ship's
officers and injuring twenty-two men. The Muavenet was written off as a result, and
the US presented them with the Knox class frigate USS Capodanno as reparations.
Evolved Sea Sparrow missile
Although the Navy and Air Force initially planned additional upgrades for the Sparrow,
notably the AIM-7R with a combination radar/infrared seeker, these were canceled in favor of the
much more advanced AIM-120 AMRAAM in December 1996. With the link between the airborne and
shipborne versions of the Sparrow severed, Raytheon proposed a much more extensive set
of upgrades to the Sea Sparrow, the RIM-7R Evolved Sea Sparrow Missile. The changes were
so extensive that the project was renamed, becoming the RIM-162 ESSM.
The ESSM takes the existing guidance section from the RIM-7P and fits it to an entirely
new rear-section. The new missile is 10 inches in diameter instead of the previous 8 inches,
which allows for a much more powerful motor. It also eliminates the mid-mounted wings entirely,
replacing them with long fins similar to those on the Standard missile and moves guidance
control to the rear fins. The tail-fin based steering of the ESSM uses up more energy but
offers considerably higher maneuverability while the engine is still firing.
The Mark 25 quad-missile pack was developed during the 1990s to fit four ESSMs into a
single Mk 41 VLS cell. For VLS use, ESSMs are fitted with the same JVC system as the
earlier versions. Operators
Australia Royal Australian Navy
Belgium Belgian Navy
Bulgaria Bulgarian Navy
Canada Royal Canadian Navy
Chile Chilean Navy
Denmark Royal Danish Navy
Germany German Navy
Greece Hellenic Navy
Italy Italian Navy
Japan Japan Maritime Self-Defense Force
Republic of Korea Republic of Korea Navy
Mexico Mexican Navy
Netherlands Royal Netherlands Navy
New Zealand Royal New Zealand Navy
Norway Royal Norwegian Navy
Portugal Portuguese Navy
Spain Spanish Navy
Turkey Turkish Naval Forces
United States United States Navy
References Notes
Bibliography Friedman, Norman. U.S. Destroyers. Naval Institute
Press. ISBN 1-55750-442-3. Polmar, Norman. The
Naval Institute Guide to the Ships and Aircraft of the U.S. Fleet. Naval Institute Press.
ISBN 1-59114-685-2. See also
List of missiles Missile designation