The original Sea Sparrow was an expedient design intended to provide short-range defensive fire in a system that could be deployed as rapidly as possible. The
AIM-7 Sparrow was the simplest solution, as its radar guidance allowed it to be fired head-on at targets. The radar signal could be provided by mounting an aircraft radar on a trainable platform on a ship. In the years after its introduction, it was upgraded to follow improvements being made in the air-to-air Sparrow models used by the
US Navy and
US Air Force. The ultimate version in this line was the R model, which introduced a new dual-seeker homing system and many other upgrades. In the air-to-air role, however, this was passed over in favor of the
AIM-120 AMRAAM, which offered much higher performance from a smaller and lighter missile. Development of the air-to-air Sparrow ended in the 1990s. Only the Sea Sparrow, therefore, remained using the basic platform — with no need to be suitable for aircraft. Rather than using the existing P and R models, it was decided to dramatically upgrade the weapon. The Evolved Sea Sparrow (ESSM) emerged as a completely new weapon, sharing only the name with the original. All of the same support equipment was used, though, allowing it to be fitted to ships already mounting the older models. Compared to the Sea Sparrow, the ESSM has a larger, more powerful
rocket motor — developed by
Orbital ATK in cooperation with
Nammo Raufoss — for increased range and agility, as well as upgraded
aerodynamics using
strakes and
skid-to-turn. In addition, the ESSM takes advantage of the latest
missile guidance technology, with different versions for
Aegis/
AN/SPY-1, Sewaco/
Active Phased Array Radar (APAR), and traditional target illumination all-the-way. In the 2000s, the NATO Seasparrow Project Office began planning an upgraded Block 2 version of the ESSM. In 2014, Canada pledged to underwrite their share of the Block 2's development cost. ESSM Block 2 leverages the existing Block 1 rocket motor and features a dual-mode
X band seeker, increased manoeuvrability, and other enhancements. Block 2 features enhanced communications systems that allow mid-course guidance correction, making the missiles easy to network into the Navy's emerging
Cooperative Engagement Capability. Unlike Block 1, Block 2's
active radar homing seeker supports terminal engagement without the launch ship's target illumination radars. The upgraded blast-fragmentation warhead was designed, developed and is being produced by
Roketsan. The improved ESSM Block II will be fielded by the US Navy from 2020. ==Launchers==