SAMs in pairs?

Good points UAZ.

There is also the issue of settings for the missiles themselves.

One of the problems for the SA-2 in for example downing B-52s or for that matter other types, was that it was found that the proximity fuse settings were a bit optimistic regarding the effectiveness of the warhead and the accuracy of the guidance. Although fitted with a very large warhead they tended to explode to far from the B-52s to adequately destroy them… something the US was very keen to keep from the Vietnamese and Soviets of course. Jamming and decoys increased miss distances which meant firing more missiles was a reaction but not necessarily a solution to these and other problems.

Just like Garry mentioned, the main reason for launching SAMs in pairs is to maximize the probability of a kill.

Statistics for an old S-125 (SA-3) are something like 75% chance of a hit for 1 missile. 95 % for 2 missiles and 98% for 3 missiles launched. By increasing the number of missiles launched simultaneously at the same target you maximize the probability of a hit. Note that the probability will never be equal to exactly 100%.

Of course, action taken by the targeted aircraft (evasive maneouvers, ECM, chaff, etc.) reduce those probabilities.

There are 2 other secondary reasons why SAMs are launched in pairs (or multiples).

1) A SAM complex has a relatively small window of time/space to shoot at an enemy plane. Second chances are rare. Since there is always the remote chance of a missile malfunctioning, better use more than 1 missile.

2) A hit by a SAM does not necessarily mean a “kill”. The targeted aircraft may be able to return to base with repairable damage. Smaller short range SAMs have small warheads. Larger SAMs are typically designed to explode in the vicinity of the target. Additional hits improve the probability of an actual “kill”.

I also thought the reasoning for firing in pairs maybe down to an aircraft’s countermeasures not being able to use directed countermeasures against two simultaneous threats or can they eaily deal with simultaneous threats? (I’ve only seen mention of testing DAS suits for example against single missiles.)

The problem is the variety of weapons/wars/situations. Take the simple Digit setup for Igla. There is a chance that flares might distract a missile. That chance is measured in a fraction of 1 and is a probability. Ie a Helo of x type with the sun glinting off the canopy disperses flares of x type creates a 0.78 probability of a kill from 3km range by an Igla missile. That means that out of 100 missiles launched 78 missiles will record hits. Well if you fire two the probability for each missile remains the same (unless the two missiles interfere with each other in flight) so the chance of one missile hitting the target remains 0.78 but because two missiles are fired you are doubling your chances of hitting the target with ONE missile. The chance of both missiles hitting is probably much lower but is also possible.

In the case of larger radar guided enemy SAMs it depends upon whose airforce and whose SAMs they are and who is supplying whom. Are wild weasel aircraft involved. Is the SAM a known system to the attacker. Have countermeasures been developed. If chaff is effective against a type of SAM then you can expect SAMs of that type to be ineffective no matter how many are fired if the chaff is used effectively at the right time. The idea that missiles can be fired blindly in volleys to shoot down planes is silly. Most missiles wont even launch without a lock and may even self destruct if lock is lost to prevent the SAM hitting something on the ground. No point in shooting down all the enemy planes with a 100% effective missile only to find the target area destroyed by errant SAMs.

Systems like the Tunguska or TOR use radar antenna to transmit guidance signals to the missile with the target being tracked with an optical tracker or radar tracker. For a threatening target like a HARM they might fire two missiles onto the same incoming target because if the target gets through there is no value in still having SAMs ready to launch…

Thanks for that info. 🙂

I also thought the reasoning for firing in pairs maybe down to an aircraft’s countermeasures not being able to use directed countermeasures against two simultaneous threats or can they eaily deal with simultaneous threats? (I’ve only seen mention of testing DAS suits for example against single missiles.)

Some SAMs are, but most are not.
Sometimes volleys are used against difficult targets, for example when Gary Powers’ U2 was shot down the Soviets fired quite a few SA-2s from several SAM batterys.
Shoulder launched missiles like Igla are generaly fired in singles and will only be fired two at a time from special launchers like Digit. (Digit is a twin launcher from Igla type manpads. They are fired at the same time but as part of their flight control algorithm they fly apart for the initial phase of flight so it was like two guys fires individual launchers from maybe a couple of dozen metres apart to prevent each missile seeker seeing the other missile.)
The number of missiles fired at once depends upon your guidance system… if it has 10 channels for one SAM battery and there are ten targets coming you you can guide 10 SAMs, one to each target, two to each of five of the targets etc etc. The advantage of two missiles at one target is probably not improved upon greatly with three missiles at the same target unless they each use a different form of guidance.

With AAMs the Soviets tended to have SARH and IRH missiles because they were complimentary and when used together increased the problems of the targetted fighter. They also improved interception capability in that the ability of radars to track targets is greatly effected by whether they are moving toward the radar or away from the radar. A closing target could be attacked at maximum range with a SARH missile but a receeding target the tracking range is much shorter. A receeding target is showing its engine nozzles however and is a much better target for IRH missiles. Heavy cloud or rain makes SARH better.