The 21-cm Nebelwerfer 42 (translating to "smoke-thrower" or "smoke launcher" and also known under the shortened designation of "21-cm NbW 42") was a battlefield artillery support system fielded by the German Army in World War 2. The weapon was designed to deliver a salvo of high-explosive rockets against enemy troop concentrations or dug-in personnel with some level of accuracy. Beyond their obvious inherent lethal capabilities, such weapons could also be called upon to unleash unseen psychological effects on those unfortunate to find themselves on the receiving end of a salvo. Eventually, between 1,487 and 1,587 examples were delivered to the German Army from 1942 to the end of the war in 1945.
Despite the basic concept of battlefield rockets being around for thousands of years, it would have to wait until World War 2 to see a true resurgence. All major powers delved into the development of such weapons with the Soviets leading the way in their practical frontline use - utilizing rockets from their famous "Katyusha" systems when setting up their massive ground offensives in an effort to "soften up" enemy areas before the initial infantry thrust. However, it was the Germans that were technological leaders in the field who, unlike the Soviets, elected to use their rocket systems as a supplementary weapon to complement their artillery barrages. As such, rockets were utilized to the highest of degrees along the East Front where the German Wehrmacht invaders squared off directly against the Red Army defenders - the pair becoming two of the largest battlefield rocket users of the war.
Despite the advanced stage of warfare in World War 2, the use of barrage rockets had inherent benefits and limitations. Rocket weapons proved cheaper to mass-produce than other dedicated systems and their psychological effects on the enemy were second to none. Warheads could be adapted to the operator's needs and delivery was quick and violent, littering a target area with explosion after explosion. However, rockets were still nothing more than launched projectiles attached to a basic "Point A-to-Point B" trajectory. As such, this trajectory was always open to outside influences greatly affecting the rockets approach from the moment of launch to the moment of impact. Couple this with uneven burning of propellant and a single rocket nary had the ability to reach a precise target and thusly forced the use of "barrage" firepower through the fielding of multiple rocket "projector" systems.
While the Treaty of Versailles forbade the development of heavy artillery for Germany, it made no impact on the development of rocket artillery. In 1931, German engineers secretly began work on several solutions to deliver explosive-, or even poison-tipped, rockets against expected enemies throughout Europe. The end result became a series of "Nebelwerfer" designs that went on to prove quite effective for the German Army in their near-future conquests. Such was the case with the implementation of the 21-cm Nebelwerfer 42 system. Its use was, on more than one occasion, a deciding factor in German victories throughout World War 2 - in the same way a machine gun in World War 1 could effectively tip the balance in the favor of its owner, so too could systems such as the Nebelwerfer 42 bring favor to the Germans.
The origins of the 21-cm Nebelwerfer 42 lay in the successes the Germans had experienced through implementation their 15-cm rocket weapons. In 1941, the engineers decided to take the 15-cm model and provide the Army with a larger caliber weapon for greater firepower, thusly giving rise to the 21-cm (210mm / 8.27 inch) Nebelwerfer of 1942. The system was ultimately delivered to units of the "Nebeltruppen", the German equivalent to the specialty American "Chemical Corps".
The 21-cm Nebelwerfer 42 utilized a collection of five mounted launch tubes fitted to the top of a carriage and organized in a "star" pattern; two tubes held close together towards the bottom of the arrangement, two spaced well-apart at the middle and the final launch tube set between and slightly above the upper most pairing with a noticeable gap in-between all tubes. The projector stand was initially to be simply an enlarged form of the basic 15-cm projector - complete with six launch tubes - but the larger caliber brought about balancing issues during transport and firing, necessitating the loss of one of the launch tubes. Each launch tube was electrically wired and triggered by way of an explosives "plunger" type activation unit. The unit was given an amount of connective cable to allow for safe firing of the weapon from a nearby, hopefully covered, location. The transport carriage on which the launch tubes sat upon was a modified form of the same one used with the PaK 35/36 anti-tank gun though fitted with a specially designed stabilizer leg at the front for additional support when firing. The carriage was fitted with two large road wheels and applicable tow "arms" to make the system highly mobile when connected to a support truck or similar vehicle. Additionally, the road wheels allowed a Nebelwerfer crew some flexibility in modifying their field-of-fire by simply pivoting the system against a new firing direction. The crew generally numbered four personnel.
Each artillery 21-cm rocket - designated as "21-cm Wurfgranate 42" - was a specially-designed projectile that externally mimicked traditional artillery ammunition. The slim nose cone provided the needed aerodynamic flow and the body was cylindrical in shape, leading to a cut-off base without any noticeable stabilizing fins. However, this external design was somewhat misleading for the warhead, normally contained in the nose cone assembly on an artillery projectile, was in fact fitted well-aft of the tip - the tip instead left hollow. The 14.3lb engine was fitted to the front of the projectile housing while twenty-two angled "venturi" were affixed to the projectile base to give it the needed spin stabilization during flight. These openings were set at 16-degree angles from axis and provided a clockwise "rifled" rotation or spin during flight. Some 22.4lbs of explosive made up the projectile's deadly payload - only high-explosive charged projectiles were ever produced for the Nebelwerfer 42 (no AP rounds were designed). However, special liner rails could be fitted inside of each launch tube to accept the 15-cm Wurfgranate 41 series rockets which, themselves, could be capped with high-explosive, smoke or even poison payloads. Additionally, rockets could be fitted with a delayed fuse or impact detonation as needed.
The firing action required the Nebelwerfer team to remove themselves from the direct vicinity of the readied launch tubes, finding cover wherever possible. When the firing order was given, a crewmember activated the launch plunger and the launch tubes responded, launching one rocket at a time in a predetermined launch order until all rockets were clear of the tubes (it is of note that the system could not single-fire individual rockets, only sets of rockets in this staggered launch fashion). The crew could then displace the projector to another location or reload fresh projectiles into each launch tube for another deadly salvo. A full salvo was unleashed in just eight seconds.
As can be expected, the Nebelwerfer 42 firing action was not without consequence; with each launched rocket there emitted a good amount of "back blast", stirring up a great deal of dust and debris while also producing smoke trails (from the rockets) in the process. This, in effect could supplying the weapon's general location to an observant enemy on the receiving end, opening the Nebelwerfer crew to a heavy artillery or like-rocket response in turn. Additionally, the rocket launch sequence provided a discernable level of noise that could be instantly recognized by the enemy, giving up the initiative to an extent. The enemy now knew the weapon type, ammunition being utilized and the approximate time for reloading. However, no one could discount the power of Nebelwerfer units as a whole, particularly when paired with other like-units or artillery, and its general effectiveness far out-weighed the battlefield dangers.
Along the East Front, Nebelwerfer systems were generally fielded alongside artillery systems for a one-two punch in support of German Army ground actions. Nebelwerfer 42s were issued in groups numbering six launchers with three groups per battalion organization and were fielded as independent brigades. Beyond the East Front, Nebelwerfer teams were unleashed against the Allies across North Africa, in occupied France and across fascist Italy, the latter after the 1943 Allied campaign.
Such was the power of the 21-cm Nebelwerfer 42, in fact, that the Americans captured intact specimens, sending them back stateside for evaluation; America generally lagged behind the other powers in design and production of similar rocket projectors. To this extent, the Americans outright copied the Nebelwefer 42 under the designation of "T36". Though this system was never placed into production, it served as a vital testbed for the US Army.
The German Luftwaffe also found value in the Nebelwerfer 42 rocket and designated it as the Werfer-Granate 21 ("WGr. 21", also "Bordrakete 21" - "BR 21") beginning in 1943. This version differed in utilizing a timed fuse with a larger warhead for affecting the large Allied bomber formations wreaking havoc on German war-making infrastructure through day and night sorties. These rockets were fitted into specially-designed single-launch, firing tubes to be utilized by German fighters, heavy fighters and dedicated "bomber destroyers".