R4M – IRGON

Testing the German R4M air-to-air rocket on Orford Ness

After the close of hostilities in Europe in 1945, the Allies gathered many German weapons and other equipment to evaluate for themselves. An example which was tested on Orford Ness (and Aberporth in Wales) is the air-to-air rocket R4M.

Background to the R4M

Responding to the worsening bomber attacks on the Reich in 1944, the RLM (Reichsluftfahrtministerium, the German Air Ministry) issued a requirement for a compact fin-stabilised air-to-air rocket which could be electrically fired. ¹ The design was taken up by the Heber/Osterode company and the Deutsche Waffen- und Munitionsfabriken at Lübeck-Schlutup.²

Much of the design was worked out by Fräulein Dr. E. Schwarz. According to Major Leslie E. Simon, who was familiar with the work of the Luftfahrtforschungsanstalt (LFA) at Braunschweig, the ballistics section under Fräulein Dr. Schwarz were carrying out much better work than the LFA. ³

The resulting weapon was a simple single-chamber solid fuel rocket, the R4M (Rakete, 4 kg, Minenkopf), was 55mm in diameter, 812 cm in length, with 8 flip out tail fins.

Tested in March 1945 under the leadership of Major Christi at Erprobungskommando 29, the R4M showed great promise. In one mission using the Me262, 25 of a group of 425 B-17 bombers were destroyed within a very short time without any losses. In April, DWM received orders to produce 25,000 R4M units with the highest priority. ⁴

Although the R4M rocket itself was a very simple weapon, its potential must be viewed as part of a system, comprising the Me262, the computing gunsight EZ42, and the ability to fire a closely spaced salvo by electrical means. The team of specialists under Fräulein Dr. Schwarz had made careful studies on the optimum range for opening combat between fighters and bombers, various armament, types of ammunition and other factors. Much data was derived from the examination of downed Allied aircraft.
Luckily for the Allies, the collapse of German industry and infrastructure meant both the Me262 and the R4M never reached the front line in meaningful numbers. Even so, sources indicate that more sorties may have been carried out than previously thought, and other aircraft (e.g. the Fw. 190D) were fitted with R4M racks. *

Artist’s impression of an Me262 about to engage B17s over Germany. © IRGON

B-24 Liberator Serial No. 44-83887 falls to the ground after an encounter with an Me 262 armed with R4M rockets, near Ludwigslust/Hamburg on 4th April 1945 © USAF

Testing on Orford Ness

The British were interested to verify the effect of the R4M on British heavy bomber airframes. They did this by firing R4M rockets from tubes on the ground. This would not have been very representative of air combat, but at least the lethality of the warhead could be estimated.

In a combat situation, the Me262 pilot would have released his salvo of rockets from a distance of 500 metres, at which distance the projectiles would have been close to their maximum velocity.

There were two types of tests made on Orford Ness:

Firing tests were made from a bazooka tube. There was probably no provision made to allow the fins to extend: normally, the R4/M was delivered with a cardboard ring around the tail, held in place by a wire. When loading the into the launch guides, the wire was removed, the cardboard ring was wrapped around seven of the fins, and then held in place by pressing in the eighth vane. The rocket was then inserted into the guide slot so that this eighth vane was clamped into the closed position. Firing the rocket without fins extended would have resulted in the “most erratic” flight reported by RAE ⁵. To mitigate this, the rockets were fired at very close range (30 yd).

After such a short distance, the projectile would have reached 195m/s after 28 metres (0.28 sec after firing)

This was a very crude test, and the rocket would have impacted the target with only around 36% of its maximum velocity (V_max was 525 m/sec).⁶

2. Static detonation trials were also carried out without the rocket motor.

Test results

Targets used were the fuselage and wing of a Handley Page Halifax, a Vickers Warwick fuselage (this aircraft was chosen in order to compare blast effects between conventional and geodetic construction). The conclusion was that a single strike about the centre of any section of an aircraft of the Halifax type would generally be structurally lethal.

Above: Test on a Warwick rear fuselage, note the geodetic construction

_{All photos copyright The National Archives. Contains public sector information licensed under the Open Government Licence v3.0.}

* Designs existed for honeycomb type launchers for the He. 162 and Ba. 349, and a photograph exists showing an Me. 163A equipped with R4M firing racks. It was also tested on the Me 110 and the Fw 190 ⁷. Other exotic projects for which the R4M was considered were the Heinkel P1077 “Julia”, the Henschel Hs P.136 and the Blohm & Voss Bv P.212 ⁸

Postscript

The unguided air-to-air rocket was briefly in vogue in the USA in the 1950s. However, the accuracy obtained was never close to what the Germans had managed to achieve with the R4M, and these rockets were rapidly abandoned in favour of the guided missiles becoming available by the late 1950s.

References