Panzerabwehrrakete X-7 Rotkäppchen
Another most advanced weapon conceived by the germans in WW II was the Panzerabwehrrakete X-7 ("tank defense rocket") anti-tank guided missile, nickname Rotkäppchen ("little red riding hood"), project number 8-347. Developments for a guided AT missile begun as early as 1941 when BMW (the car company) offered the weapon to the army's weapons bureau. Because of the then generally good military war situation the army wanted to save the projected development costs of 798,000 RM. In 1942 Dr.Kramer of the german research institute for aircraft developed rocket engines for weapons that resulted in the X-series of guided bombs and precision weaponry of which the X-7 was the smallest family member.
The first prototype was followed by a larger production model with a changed detonator for the shaped charge of 2.5 kg. The back part of the main body (length 46.5 cm; diameter 15 cm)contained the two-stage solid fuel rocket engine 109-506 developed and made by the company WASAG. The wings were swept forward and had wingtips which housed the guidance wires, wingspan was 60cm. The small elevator/steering rudder assembly was set off 13.2 cm of the main body's axis. Total length including the protruding detonator cap (diameter: 3.8 cm) was 95cm. The fully loaded Rotkäppchen weighed 9kg.
The missile was to be launched from a start rail tripod that was 150cm long and weighed 15kg. the missile's rocket engine was ignited with a 300V battery. This fired the 2g gunpowder positioned in the two hollow half rounds of the gyro stabilizer. the explosion gases exited through two tangential openings and immediately brought the gyro to operating speed. Then the 3kg of propellant of the first stage of the rocket engine were ignited. They developed 68kp thrust and accelerated the missile to it's flight speed of 98m/s in 2.5 sec.
In flight the X-7 rotated around it's axis at a rate of two rotations/sec. Guidance commands from the gunner were transmitted over the two wires, one for longitudinal and one for lateral corrections. A delay mechanism let the steering rudder of the elevator only work when it was in the right position for the respective command, in other words, the elevator worked both as a (longitudinal) elevator and a (lateral) rudder. Guidance was achieved through optical tracking of the small tracer in the rear of the rocket that was to be kept superimposed over the target by the gunner's commands until it impacted (a method still in use today and known as CLOS for command-line-of-sight).
The second stage of the rocket engine developed a thrust of 6kg for 8sec. This sufficed to keep up a speed of over 300km/h and reach a range of 1200m. The shaped charge warhead was strong enough for all known tanks of that era.
A trial was undertaken on September 21st 1944 with seven X-7 missiles. Because of the unusual and unfamiliar flying characteristics the first four weapons had ground contact after some distance and therefore crashed. On the next two the rocket engine exploded on the way to the target. The last Rotkäppchen flew all the way and hit the target tank at a range of 500m dead center.
Only about 300 X-7 Rotkäppchen were completed; mass production was planned and had already started at the companies Ruhrstahlwerke in Brackwede and the Mechanische Werke in Neubrandenburg. Many almost finished weapons were captured by the allies.
It is unclear whether the combat trial at the front took place or which results it had.

Improvements of the X-7 Rotkäppchen were the Steinbock which used infra-red transmitting of the guidance command and therefore didn't require the wires. An automated tracking device was the Pfeifenkopf or Pinsel project. It utilised a machine that computed the changes in angle of the two sighting devices - one was to be aimed at the target, the other at the missile- into commands for the missile. This mechanism was further atomated in the Zielsuchgerät ("target aquisition device"). By using an image recognition device called Ikonoskop the missile was to seek its target through it's own optical sensor that compared the image data from the aiming device with the data it received from its own optical sensor.
Besides these avionics and electronic equipment, other long range ATGMs were the Rochen-600, Rochen-1000 and Rochen-2000 for ranges of 500m , 1500m and 3000m respectively. Another project called Flunder utilized many parts of the Panzerfaust including it's warhead and using it's launch tube for the rocket engine. None of these projects were completed.
 

Panzerabwehrrakete Ruhrstahl X-4

The Ruhrstahl X-4 with the project number 8-344, another project by Dr. Kramer, was originally intended as a guided air-to-air missile. At first it was envisioned as air intercept missile for the smaller daytime fighters, especially the Me-262 jet. However, the Luftwaffe instead opted for the unguided R4M air-to-air rocket and declared the X-4 to be used by larger, multi-engine aircraft. In November 1944 it was decided to examine the use of the X-4 as an antitank weapon.
For this new role, the acoustic target proximity fuse "Kranich", also called "Dogge", that was tuned to the bomber aircraft engines was removed, which resulted in a much shorter overall length of 169cm instead of 200cm for the AAM; still, the X-4 was considerably larger than the X-7. Also, the large 20kg explosive warhead used for the aircraft weapon was substituted with a large shaped charge for the anti-tank role. The missile had a diameter of 22cm and four large fins in the middle and four small fins at the rear. The wingspan was 78cm; two of the wingtips carried small containers for the guidance control wires. The weapon was steered with a little joystick. A small tracer at the rear of the weapon was to be kept superimposed over the target by the gunner until the missile impacted.

The rocket engine was built by BMW under the designation 109-448 or 109-548 and used a mix of S-Stoff (nitric acid with 5% iron(3)chloride) and R-Stoff (an organic amine-mixture of 50% dimethylaminobenzene and 50% triethylamine called Tonka 250) as propellant. When these two fuels contacted each other in a mix of 3.7:1 they reacted without outside ignition. The rocket engine developed 140kg thrust. A problem was the S-Stoff that was so aggressive that it dissolved all base metals; in the rocket itself the S-Stoff tank was made of Pantal. Because of the problems this posed in producing and handling the weapon, it was projected to substitute this rocket engine with a solid-fuel rocket engine in the future mass production. The X-4 carried 6.7kg S-Stoff and 1.8kg R-Stoff which made for a range of roughly 4000m.

In flight, the rocket rotated at a rate of about 360° per second to compensate for inaccuracies steming from production or other flaws. The weapon reached a flight speed of 240m/s.

950 X-4 were produced by the company Ruhrstahlwerke in Brackwede until the end of 1944. The respective engines were built by BMW in Berlin and the Gerätewerke in Stargard at a total number of about 1,500. Very probably all of these were of the original aircraft-weapon - version; most of them were used up in trials.

For further information on the Air-toAir missile variant of the X-4 I can highly recommend Ray Corridon's X-4 - page, it features several detail pictures of a restored X-4 AAM as well as the american foreign Ordnance Publication document on the X-4. You might also want to try the USAF museum's page on the X-4. Pictures of other german aircraft-related rocket projects can be found at Phil Callihan's Missiles-Rockets-Bombs - page.

 
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