Editing R4M (section)

== Development ==
{{More citations needed section|date=September 2021}}
The R4M was developed in order to deal with the increasing weight of anti-bomber weapons being deployed by Luftwaffe fighters. The primary anti-bomber weapon of the Luftwaffe for much of the war was the 20&nbsp;mm [[MG 151/20 cannon|MG 151/20]] [[autocannon]], which was compact enough to be mounted in an internal wing bay mounting in the [[Focke-Wulf Fw 190]] (up to 4 cannon, or 6 with optional twin-gun underwing pods) and also fitted on the centerline of [[Messerschmitt Bf 109|Bf 109G]] fighters, firing through the propeller spinner as a ''Motorkanone''. This could be supplemented by an additional pair of cannon in drag-inducing underwing [[gun pod]]s, but it was found that it took an average of twenty 20&nbsp;mm hits to shoot down a typical four-engined Allied bomber. The MG 151/20 was subsequently supplemented with or replaced by the 30&nbsp;mm [[MK 108 cannon]], which replaced the centerline ''Motorkanone''-mount MG 151/20 on many Bf 109's, and could be fitted into slightly larger underwing pods, which could be used on either the Bf 109 or Fw 190. This heavier-[[Caliber (artillery)|caliber]] cannon could bring down a bomber with an average of one to three hits. However, the [[MK 108 cannon|MK 108]] was much heavier and the larger calibre ammunition made it difficult to carry more than one or two "passes" worth. Worse, the low [[muzzle velocity]] of this gun meant it had a very short range and suffered a [[bullet drop|ballistic drop]] of over 41 metres at 1,000 metres range after firing. In approaching close enough to get hits, the fighters placed themselves within the range of the dozens of [[M2 Browning#Aircraft guns|AN/M2 "light barrel" Browning]] defensive machine guns that a combat box formation of a typical USAAF heavy bomber raid possessed, from nearly any approach direction. The more powerful [[MK 103 cannon]] had higher muzzle velocity and increased range, at the cost of greatly increased weight, size (barrel length of 1.34 meters, or 52-3/4 inches) and much lower rate of fire: 380-420 RPM vs. 600-650 RPM for the [[MK 108 cannon|MK 108]].

Also, the [[21 cm Nebelwerfer 42|Nebelwerfer]] 42-derived ''[[Werfer-Granate 21]]'' (Wfr. Gr. 21, or ''Bordrakete'' BR 21) rockets fitted to Messerschmitt Bf 109 and [[Messerschmitt Bf 110|Bf 110]], and Focke-Wulf Fw 190 fighters, used to break up the [[United States Army Air Forces|USAAF]] [[combat box]] bomber formations, had launch tubes that were not only drag-producing, due to their exposed five-strut under-wing mounting, but also from the fact that the launch tubes needed to be aimed upwards at some 15° from level flight, to counter the BR 21 rocket projectile's considerable ballistic drop after firing. This added to the already considerable drag the launch tube mountings created, and contributed to the Wfr. Gr 21's relatively slow projectile velocity of {{Convert | 1150 | km/h | m/s mph | abbr = on}}, approximately 60% of the {{Convert | 505 | m/s | mph | -1 | abbr = on}} velocity of the [[MK 108 cannon]]'s shells.

The solution was to replace the underwing gun pods, and the excessively drag-producing large-calibre underwing rocket launch tubes, with a small-diameter solid-fuel rocket-engine-propelled projectile, mounting a warhead similar to that of the cannon shell. Although each "round" was heavier than the corresponding gun-fired shell, the absence of a gun reduced the overall weight considerably. The weight difference was so great that even a much larger and longer-ranged rocket was still lighter than the guns it could replace, although the total number of rounds carried was also reduced from 65 rounds of 30&nbsp;mm ammunition to only 24 rockets.

[[File:R4M AT version.jpg|thumb|upright=1.0|left|Anti-tank version of the R4M rocket on display at the [[Steven F. Udvar-Hazy Center]].]]
The anti-aircraft version of the R4M used a large warhead of 55&nbsp;mm with {{Convert | 520 | g | abbr = on}} of the strongly [[Brisance|brisant]] [[Hexogen]] explosive charge, nearly guaranteeing a fighter kill with one hit, from the "shattering" force of its explosive warhead — this was the same explosive used in the shells fired by both the [[MK 103 cannon|MK 103]] (30&nbsp;x&nbsp;184&nbsp;mm cartridge) and [[MK 108 cannon|MK 108]] (30&nbsp;x&nbsp;90&nbsp;mm cartridge) autocannons. Each R4M weighed 3.2&nbsp;kg and was provided with enough fuel to be fired from 1000&nbsp;m, just outside the range of the bomber's defensive guns. The main body of the rocket consisted of a simple steel tube with eight base-hinged flip-out fins on the tail for stabilisation (patented by [[Edgar Brandt]] in 1930<ref>{{US patent|1879840A}}</ref> and also used on the contemporary [[M8 rocket]]), deployed immediately after launch. A battery typically consisted of two groups of 12 rockets and when all 24 were salvoed in an attack, they would fill an area about 15 by 30&nbsp;m at 1000&nbsp;m, a density that made it almost certain that the target would be hit. The R4Ms were usually fired in four salvos of six missiles at intervals of 70 milliseconds from a range of 600&nbsp;m, and would supersonically streak towards their target at a sixty percent higher velocity than the [[Werfer-Granate 21|Wfr. Gr. 21]]'s rockets would (the BR 21's projectile travelled at some 1150&nbsp;km/h post-launch), as the R4M typically had a flight speed of roughly {{Convert | 1890 | km/h | abbr = on}}. Two warheads were available for the R4M, the common '''PB-3''' with a 0.4&nbsp;kg charge for [[anti-aircraft]] use and the larger shaped charge, similar in construction to the [[Panzerschreck]], the [[Panzerblitz (missile)|Panzerblitz]] (PB-2/3), for [[anti-tank]] use. The ''Panzerblitz III'', mounting a gigantic 210&nbsp;mm [[hollow charge]] warhead (the same calibre as the BR 21), can be seen as the ultimate development of the basic ''Orkan'' rocket. It was intended to be carried (six or eight rockets per plane) by the [[Anti-tank rocket|tank-busting]] B model of the [[Henschel Hs 132]] jet [[dive-bomber]] - however, neither the missile nor the warplane it was exclusively intended for got beyond the prototype stage before the end of the war.