Battlefield missile artillery from the blackpowder age to the 21st century - Part I

Rockets became feasible with the invention of blackpowder or similar mixtures hundreds of years ago. They are about as old as guns, but weren't able to rival guns successfully until the 20th century.

The propulsion energy comes from the rocket fuel (solid or liquid) and the nozzle shape, but the stabilization is what makes them useful and predictable. Two methods of stabilisation are now dominant (fin stabilisation and different kinds of spin stabilisation), but others such as a centre of gravity behind the nozzle (as with modern consumer fireworks) were actually more relevant among the recurring attempts to produce competitive battlefield rockets till the early 20th century.

Fin stabilisation is the most interesting one, as it is of more simple and lighter design than typical spins stabilisation for rockets and it's dissimilar to the (now rifled) guns' spin stabilised shells. The differences includes some advantages:
(1) Fin stabilisation is easily adaptable to guidance, as steering can be done with simple rudders.
(2) Fin stabilisation begins to work well at a length:diameter ratio of 7:1, while a 100% spin stabilisation becomes rather impractical with such lengths. As a result, fin stabilised rockets can be very long and thus have a very large volume.
It is possible to combine fin and spin stabilization, often with a slow spin used to stabilize during the early acceleration phase when the velocity-dependent fin stabilization isn't very effective yet. Such combined stabilisation uses angled nozzles, angled fins or a rifled launcher tube.

Rockets have in general several advantages over guns as well:
(a) Very low cost of launcher for a rapid fire capability (the simple BM-21 multiple rocket launcher (MRL) launches 122 mm rockets at 0.5 second intervals while the largest gun with such a rate of fire is a heavy and elaborate 76 mm naval gun)
(b) Very low cost of launcher for a very long range (as evidenced by the lack of a gun equivalent for intercontinental missiles)
(c) Low cost of launchers in general (unless you mess up a procurement project and end up paying military prices for standard hydraulics).
(d) Submunition dispersion is more controllable than with most tube artillery. Fin-stabilised rockets can still spin slowly at the angular speed required for the desired dispersion of submunitions. Spin-stabilised warheads need to spin quickly at all times.

There are important disadvantages as well, though:
(I) Rockets have unlike howitzers and mortars no variable propellant power. You can thus not reduce the charge for short-range shots. Some multiple rocket launcher (MRL) rockets are available with air brake attachments to be added to the nose for this reason; the air brake reduces their range and thus their otherwise often too long minimum firing distance). High-end rockets have actually variable propulsion (liquid fuelled ones and restartable solid fuel rockets), but these are too elaborate for quantity-produced battlefield artillery rockets.
(II) Highly visible firing signatures, especially if no low-smoke propellant was used.
(III) Most MRL types are unsuitable for very limited, unpredictable firing missions. You cannot expect a MRLS system which gets its rocket ammunition in sealed pods to help out with a single illumination rocket, while a mortar could (within its range).
(IV) Propulsion is less efficient than with guns; you need more chemical energy for the same projectile kinetic energy at the muzzle. This disadvantage is shared with recoilless guns, which are technically in between rockets and guns.

The earliest war rockets were devised in China and used mostly to spread confusion and fear with their unknown visual and audio appearance. The Koreans devised multiple rocket launchers using centre of gravity-stabilised rockets, called Hwacha, in the 15th century.

Hwacha reconstruction, (c) draq
The practical battlefield rockets of the 19th century were mostly the illumination rockets, which already used an early kind of parachute. Iron-cased rockets were developed in India during the 18th century and used to good effect, which led to some use of rockets during the Napoleonic Wars.

Napoleonic-era Congreve rockets

The practical First World War rocket was either a small one for illumination, signalling or incendiary purposes or a rather big one with great explosive power. Advantages (2) and (c) enabled these.

The inter-War Years saw advances towards rockets as we know them today, albeit with very poor dispersion. The Soviet Union focused on fin-stabilised rockets and Germany focused on spin-stabilised ones.*
Eventually, the smaller calibre and lower weight of most Soviet rockets led to their employment as an area weapon with great morale effect.

Soviet BM-13 (132 mm) Katyusha (c) ChrisO
The German path led to very large warheads with great explosive power or a rather large incendiary (oil) payload. Their effect on morale was great as well. Both Soviet and German battlefield rocketry was very short ranged, shorter in range than even early First World War howitzers indeed. The short range combined with the very high visibility (smoke) led to a preference for relatively expensive self-propelled (motorized) launchers. It was simply too dangerous to stay at the battery site for long after it had fired its salvo.

German 15 cm Nebelwerfer rocket - no simple design at all
Interestingly, the revolutionary R4/m rocket in use with the Luftwaffe in late WW2 pioneered folding fins for rockets. The German army stuck with complicated spin-stabilized rockets with angled spin-inducing nozzles between warhead (actually, tail) and solid rocket fuel.

The high dispersion due to insufficient stabilization of the Soviet fin-stabilised RS and BM series of WW2 rockets was caused by the insufficient stabilization during the launch phase and due to fin stabilization not being well-understood; engineers at that time basically guessed the needed fin size and shape and observed the resulting dispersion. Other fin-stabilized rockets of the WW2 era had a satisfactory dispersion of less than 1% of range.

The battlefield artillery rockets of WW2 - fired by multiple rocket launchers - were thus short-ranged, high dispersion, inaccurate salvo weapons with a high morale effect against not-yet hardened troops. The typical warhead was a high explosive warhead, with some incendiary and large blast warheads used with the larger calibres.

later Part II: Cold War battlefield rocket artillery


(unavoidable picture for fun)

*: The non-battlefield rockets such as the A-4 are outside the scope of this text. They had a combined thrust vectoring (launch control) and fin stabilisation with gyroscope and rudders for trajectory control.

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