Surface-to-air missile

Shipborne systems followed the evolution of land-based models, starting with long-range weapons and steadily evolving toward smaller designs to provide a layered defence.

[3] During World War II, efforts were started to develop surface-to-air missiles as it was generally considered that flak was of little use against bombers of ever-increasing performance.

The lethal radius of a flak shell is fairly small, and the chance of delivering a "hit" is essentially a fixed percentage per round.

[5] This potential was already obvious by 1942, when Walther von Axthelm outlined the growing problems with flak defences that he predicted would soon be dealing with "aircraft speeds and flight altitudes [that] will gradually reach 1,000 km/h (620 mph) and between 10,000–15,000 m (33,000–49,000 ft).

"[5][nb 1] This was seen generally; in November 1943 the Director of Gunnery Division of the Royal Navy concluded that guns would be useless against jets, stating "No projectile of which control is lost when it leaves the ship can be of any use to us in this matter."

In February, Friederich Halder proposed a "flak rocket" concept, which led Walter Dornberger to ask Wernher von Braun to prepare a study on a guided missile able to reach between 15,000 and 18,000 m (49,000 and 59,000 ft) altitude.

Von Braun became convinced a better solution was a crewed rocket interceptor, and said as much to the director of the T-Amt, Roluf Lucht, in July.

The directors of the Luftwaffe flak arm were not interested in crewed aircraft, and the resulting disagreements between the teams delayed serious consideration of a SAM for two years.

[7] By this point serious studies by the Peenemünde team had been prepared, and several rocket designs had been proposed, including 1940's Feuerlilie, and 1941's Wasserfall and Henschel Hs 117 Schmetterling.

One set of designs would be boosted to altitude in front of the bombers and then flown towards them on a head-on approach at low speeds comparable to crewed aircraft.

Both types used radio control for guidance, either by eye, or by comparing the returns of the missile and target on a single radar screen.

[9] The British developed unguided antiaircraft rockets (operated under the name Z Battery) close to the start of World War II, but the air superiority usually held by the Allies meant that the demand for similar weapons was not as acute.

These weapons were released from stand-off distances, with the bomber remaining outside the range of the ship's antiaircraft guns, and the missiles themselves were too small and fast to be attacked effectively.

[10] The initial performance goal was to target an intercept at a horizontal range of 10 miles (16 km) and 30,000 feet (9,100 m) altitude, with a 300 to 600 pounds (140 to 270 kg) warhead for a 30 to 60 percent kill probability.

[12] Heavy shipping losses to kamikaze attacks during the Liberation of the Philippines and the Battle of Okinawa provided additional incentive for guided missile development.

Led by Bell Labs, the Nike Ajax was tested in production form in 1952, becoming the first operational SAM system when it was activated in March 1954.

[16] Concerns about Ajax's ability to deal with formations of aircraft led to greatly updated version of the same basic design entering service in 1958 as the Nike Hercules, the first nuclear-armed SAM.

[16] The U.S. Army Air Forces had also considered collision-course weapons (like the German radio-controlled concepts) and launched Project Thumper in 1946.

The RSD 58 used beam riding guidance, which has limited performance against high-speed aircraft, as the missile is unable to "lead" the target to a collision point.

These efforts picked up again with the opening of the Cold War, following the "Stage Plan" of improving UK air defences with new radars, fighters and missiles.

Two competing designs were proposed for "Stage 1", based on common radar and control units, and these emerged as the RAF's Bristol Bloodhound in 1958,[25] and the Army's English Electric Thunderbird in 1959.

[26] A third design followed the American Bumblebee efforts in terms of role and timeline, and entered service in 1961 as the Sea Slug.

[30] By the conclusion of the Linebacker II campaign, the shootdown rate of the S-75 against the B-52s was 7.52% (15 B-52s were shot down, 5 B-52s were heavily damaged for 266 missiles)[31] During the war, The Soviet Union supplied 7,658 SAMs to North Vietnam, and their defense forces conducted about 5,800 launches, usually in multiples of three.

As their targets were now being forced to fly lower due to the presence of the larger missiles, engagements would necessarily be at short ranges, and occur quickly.

The UK's Sea Cat was an early example that was designed specifically to replace the Bofors 40 mm gun on its mount, and became the first operational point-defense SAM.

Many of these are adapted from earlier mobile designs, but the special needs of the naval role has resulted in the continued existence of many custom missiles.

Modern long-range weapons include the MIM-104 Patriot and S-300 systems, which have effective ranges on the order of 150 km (93 mi) and offer relatively good mobility and short unlimbering times.

These compare with older systems with similar or less range, like the MIM-14 Nike Hercules or S-75 Dvina, which required fixed sites of considerable size.

The multi-stage interceptor consists of a solid-fuel, rocket motor booster, followed by an asymmetrical kill vehicle with advanced steering for super-maneuverability during the kill-stage.

Likewise, the UK's Rapier system included a simple radar that displayed the rough direction of a target on a series of lamps arranged in a circle.