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81 mm mortar [mortier van 8]

Introduction

Like many armies during the interbellum, the Dutch introduced the post WWI mortar based on the Stokes-Brandt principle in their ranks. This combination of patent-designs is most peculiar. We shall elaborate on this a little more before we address the weapon itself.

Historical prelude

The British designer (Sir) Frederick Wilfrid Scott Stokes [1860-1927] invented the light portable mortar design that nowadays still forms the basis of basically all mortars in the world. Up to the moment that Stokes introduced his invention, mortars were heavy trench weaponry that were more like short barrelled howitzers than the portable mortar we know nowadays. Stokes was a civil engineer and in 1914 [when he introduced his weapon] chairman and director of Ransomes & Rapier engineering company in Ipswich, UK, that was a major crane manufacturer.

Curiously enough the Stokes design was first rejected by the British War Department. The latter were of the opinion that the odd calibre would cause to much logistical challenges, for it would add yet another calibre to the already much extended variety in the arsenals. The Stokes design was however firmly backed by top-military officials and as such first made its way to the trenches in France in 1915.

Mortars were amongst the first of weapons the world got to know when powder was introduced on the battlefield. The ancient mortar was especially known as a defensive weapon fired from fortresses and sieged town-walls. The steep curve of the projectile made it an ideal weapons-platform for siege-warfare. Up to the Napoleontic wars it remained a prime artillery weapon. Napoleon however - being a master of dynamic warfare - saw little use for this device and focussed on highly mobile guns and howitzers.

With the trench warfare of WWI one saw the revival of the mortar. It were the Germans that showed plenty of inventiveness in development of new heavy field mortars, often mechanised in some way. They called the heavy devices "mörsers" and the medium and light types "granatwerfers". These weapons were often still heavy platforms, often hard to transport, but ideal for accurate shelling of covered positions. Besides, the 'mörsers' were breech-loaded, and as such in fact short barrelled howitzers that were however able to deliver in a steep angle.

The Stokes design would in fact mean that the gunners would fall back to ancient operation of muzzle loading. The design was very basic. In fact the Stokes mortar was nothing more [or less] than an assembly of three components [tube, base plate and bipod] that could be transported relatively easy by a three men crew. A huge leap forward in dynamic application of heavier infantry weapons.

The original design was based on a smooth bore pipe [barrel] of 3.2 inches diameter [8,14 cm]. This pipe was attached to a base plate. The pipe itself was supported by a bipod with a t-shaped screw-adjustment device for elevation [up- and down screw] and traverse [left- to right screw]. Stokes prepared an identical design of 4.2 inch diameter [10,5 cm].

The Stokes design was based on the delivery of an unstabilized cylindrical projectile [fitted with two sliding rings] of about 4,5 kgs which was entirely self-contained. The propellant was concentrated in the back of the projectile. When the projectile was released from the muzzle by the gunner, it slighted down the tube and eventually hit the fixed pin down the base. This pin activated the initiating charge-cartridge after which the ignition of the propellant followed, launching the projectile from the tube. The projectile was armed whilst on the way to the target [timer fuse], and detonated on impact.

The smooth cylindrical projectile and the lack of an aiming device made the weapon quite inaccurate to aim. Only well trained and experienced crews were able to deliver on or close to the target, but still accuracy remained low. The huge advantage of the easy-to-handle weapon made it however a tremendous success. The Stokes mortar was able of producing long sustained rapid fire of about 20 rounds a minute, and deliver those over a distance of about 1,100 meters.

After WWI the [well known] French art deco designer Edgar William Brandt [1880-1960, his father had American roots] - owner of a mechanical iron works inherited from his father - developed a fin-stabilized projectile. Also, designers of his company came with a collimator aiming device. Both new features enhanced and raised the total design of weapon and projectile to such extend that from then on the world would speak of the Brandt-Stokes patented design for mortars of 3" and 4". Designs that survive until today for all mortars of these calibres.

Brandt added the finned tail-end to the original projectile and also incorporated a gas check system in the rings around the grenade. These devices improved the grenade guidance in the tube and highly improved the projectile stability and ranging in flight. In combination with the [mechanical] collimator [device on which the projectile target can be fixed by adjusting the weapon-trims to match the target in sight] the mortar had then become a very accurate weapon.

During the interbellum almost all armies in the world adopted the French-British design for light and medium mortars of 81 mm and 105 mm. The French mass production of the weapons started in 1927, and in Europe all nations would either buy these products directly, or produce them on licences. Other countries, like Germany and Russia, produced their own spin-off designs.

The accuracy and range of the weapon differed between countries. Many local weapon producers also produced their own ammunitions and slight differences in fins, gas regulating rings and propellant caused distinction in range and accuracy of the respective weapons.

Dutch mortars

The Dutch purchased 60 mortars from the Brandt company itself in the late 1920's, and ordered 200 more to be built on a license at HIH Siderius [Rheinmetall daughter] in The Netherlands. At least 100 more were produced in the 1930's by the Dutch Artillerie Inrichtingen, and another follow-up order was placed in 1939-1940. The Dutch produced their own ammunition. The origin of the Dutch used collimator is not known, but possibly the Dutch companies Nedinsco or Nederlandse Optiekfabriek delivered these devices.

Click here for larger picture
The standard 8,1 cm mortar of the Dutch army (may 1940)

The Dutch mortars could fire three sorts of ammunitions: HE [3.25 kg] and illumination / smoke rounds. The exact range of the Dutch mortar is not known. Basically the Brandt-Stokes designs of those days had a maximum range of 2,200-2,400 meters. Straddle at the maximum range was quite considerable at about 65 meters [at 2,200 metres].

Although the rapid fire capacity of the mortar is one of its key-qualities, the Dutch army had no more than 820 rounds per mortar on stock in May 1940. Easy to predict that this was a very low figure and would later cause the active front units to run out of ammo within no time. Bearing in mind that 20 rounds a minute could be fired, the rations were only sufficient for 40 minutes of sustained action. It was a clear show of lacking vision at the military top about what weapons would really contribute to frontline efforts. At the Grebbeline for example, where the battle raged on for three days in a row, the mortar teams were out of ammo after two days of (very modest) action. Their assistance was already choked to a minimum due to the knowledge of dramatic ammo shortages in the arsenals, but even after rationing their fire missions, all mortars had fired their last rounds well before the final German push was unleashed in the morning of the 13th ...

The Dutch army was very poorly equipped with infantry support weapons, and obviously this shortage included the availability of mortars in front-line units. Every regiment [comprising three infantry battalions plus support troops; 2,500 men] had only one company of mortars at its disposal. Such a company comprised six pieces of 81 mm and 90 men. It is perfectly clear that these six mortars were almost neglectable numbers if one considers that one battalion had to defend a front width of 1,000-1,250 meters. That meant that only two mortars were available per front-sector! If one compares the amount of French and German 81 cm mortars available in May 1940 [8,000 and 6,200 respectively] - bearing in mind that both countries also used other calibres in large numbers [the Germans for example also had about 6,000 mortars of 5 cm at 10 May 1940] - one realizes that the Dutch number of available mortars was dramatically low.

The Germans gladly made use of all the captured mortars in France, Belgian and Holland that were all constructed according to the Brandt-Stokes design. The Germans were able to use these weapons instantly, for there own mortar [Granatwerfer W.34] was almost identical and could easily fire the ammunitions captured from the conquered countries. The thousands of captured mortars were quickly assigned to German troops.

The Russians - who also copied the Brandt-Stokes principle - were however clever enough to produce 8,2 cm mortars. That meant that the slight diameter difference presented them the advantageous option to use Allied [and German] ammo, but the latter could not use their ammo. Clever thinking and bearing in mind the developments in 1941 and 1942, very practical too.

Specifications

Manufacturer:  Brandt [France] 60 off
HIH Siderius [Netherlands] 200 off
AI [Netherlands] 100+ off
Design:  Brandt Stokes M.27/31
Weight [all three pieces]:  59 kg
Barrel length:  1114 mm [14 calibres]
Calibre:  81,4 mm
Max elevation:  85°
Max declination:  45°
Max traverse:  +11° / - 11°
Ammo:  HE round [3.25 net]
Illumination / smoke
Fire rate:  20 rounds a minute max
V0 HE:  160 m/sec
Max effective range HE:  2,700 m
Number in use 1940:  Approx. 400
Crew:  3 + commander