125 mm and 150 mm fortress guns
Introduction
During the 1880's the Dutch army had procured a vast arsenal of the latest generation of guns used in fortified positions, and as such designated as 'Vesting Geschut' [Fortress Artillery]. It were the 12,5 and 15 cm steel guns of Krupp, which were very notable due to their extremely high undercarriage.
The expanded Dutch ambitions to purchase new artillery had mostly seen itself strand on the issue of late decision making. As such the Dutch were basically last in line and received many declines on their inquiries from the major gun makers abroad. Bofors was one of the first to decline Dutch inquiries for new guns, so were the French and British manufactureres. As a consequence the Dutch ended up buying new artillery in Germany - ordering that is; because actual deliveries were obviously hampered by German doing. The armes control office in Germany would not have their own products taking aim at German soldiers obviously.
The late Dutch procurement of modern medium artillery - and as such the shortage of these means when the army mobilized late 1939 - forced the Dutch artillery command to hold on to the good old Krupp guns of a former generation. As such the 60-years old 12,5 cm fortress guns were still in the organisation in 1939. Their slightly bigger 15 cm 'siblings' had been mothballed ages ago, but realizing that there was a clear shortage of artillery, 52 off these guns were overhauled and reinstated in active duty in three hastily formed artillery batallions (leaving 12 off guns as a material reserve, 4 off as a school battery), mostly manned by recruits and candidate officers. After all, necessity knows no law ...!
Prelude
When the industrial revolution in the late 19th century accelerated the developments of modern weaponry, the Dutch army filed its requirement as to the modernisation of its heavier artillery segment. In those days the leaps in weapons development could make former generations of weapons obsolete in a decade or so. In the late nineteenhundreds particularly the metal developments caused weapon generations to be write offs in no time. The 1860-1880 era was notable for its leap from iron to bronze and consequently low alloy steel guns. In the next era of about 30 years better alloys caused much better guns to become available. Along with the developments of alloys went the developments of propellants and explosives, as well as projectiles and breech-mechanisms. The development of guns in the era 1860-1920 was by far the most accelerated era of the entire life-time of canons and guns.
Since the formidable Pruissian successes in the War on France in 1870-1871, the Krupp guns were considered state of the art. This well known 19th century war caused many armies to modernize its arsenals. In the 1880's the Dutch artillery selection board needed to make a choice for a new (static) artillery piece for the fortress artillery. In those days most of the army was still a static defense force with only a mild role for the more dynamic field army. As such artillery was separated into fortress artillery (static defenses and fortresses) and field artillery (field army).
The Dutch selected the 12,5 and 15 cm Krupp products that had just come available from a new range of steel fortress artillery. Both guns were then state of the art fortress weapons, that (with their high undercarriage) were clearly designated to be used in fortified positions and from large dug-outs. The guns were constructed with undercarriages with a heigth of more than 1,5m on top of which the barrel was mounted. Their weight was massive, up to 5 tons of steel, which made the guns very rigid and hard to displace. Since the rigid undercarriage was unable to traverse mechanically, the guns were only practical for delivering fire on static targets or designated area's.
Specifics
The guns were all steel products, capable of delivering canister, HE canister and HE grenades with a maximum range of 8,500m [HE 12,5 cm] and 8,800m [HE 15 cm]. The gun operation was extremely intensive and complex though, which resulted in terribly slow firing rates [3 rds/2 min for the 12 cm; 1 rd/min for the 15 cm].
The guns were of the traditional design, which incorporated a fixed under-carriage, tilting barrel and a tremendous recoil action, demanding extensive gun bed preparation. The guns were not capable of mechanical traverse, hence physical disposition was demanded to re-aim. The traverse adjustment was a terrible operation for it had to be done by physically moving the gun aside. The 12,5 cm gun weighted 3,540 kg and the 15 cm 4,700 kg. Such masses were hard to move even with the long yokes available. A minor directional change demanded a fifteen minute operation. Major direction changes demanded an entire re-positioning of gun and gun-bed, taking at least half a day if no alternative positions had been prepared (usually though, at least two or three positions in different angles had been prepared).
The 12 cm guns had been modified after WWI. Particularly the breech and gasket (seal) arrangements had been modified. That had not been the case with the 15 cm guns, that had only received some basic overhaul of existing pieces, like the trigger-sections and seals. The 12 cm modernizations would pay off, there where the minimalistic approach that was chosen for the 15 cm would cause a very high under-performance and much mechanical gun failure.
The tremendous recoil action that resulted from firing the gun required huge wooden wedges to be placed behind the giant steel wheels in order to brake the action, causing the gun to wiggle between rest and wedge a couple of times after firing. Usually ropes were attached to the wheel axis in order to trim the gun after firing, so that it could be assisted to be brought back into position soonest.
The utilization of the guns in May 1940 - as static field guns - required large gun pits to be dug-out, facilitating the guns to be brought into a wider angle without the immediate demand for a position change. An ever bigger challenge was the fact that the 12,5 cm and 15 cm guns lacked any own traction in the organisation. Originally the 12 cm had been pulled into place by 6 heavy or 8 ordinary horses a piece, but this traction was not available due to shortage of horses in the army period. In other words, they were depending on borrowing traction from other units, if these were around. This resulted in towing the guns in their projected positions long before the war had started, which increased the chances of early discovery by German intelligence gathering. The worst side effect was that displacement of the guns in war time would take ages and require traction to make the hazardous journey to and from the batteries too.
The ammunition of both guns, more specifically the charges, was basically old, mostly overdue and therefore unrealiable. This was clearly shown during the war days when many grenades fell remarkably short of target. Also the projectiles themselves were of such vintage composition that the detonating power was often less than of a contemporary light calibre shell. Bearing in mind that - certainly after some action - many seals and gaskets in the breech-arrangements started leaking, it is clear that the ranging of these old guns, particularly the 15 cm pieces, was reported as poor.
Of the 12,5 cm guns no less than 144 off were active in May 1940. A few dozen of these indeed saw extensive action. Particularly in the Betuwe-line and the southern sector of the Grebbe-line the 12,5 cm guns contributed considerably to the provided artillery support. They did perform quite well - against all odds.
The 15 cm guns - of which 52 had been activated - 36 off were assigned in a total of three active battalions. All three these battalions were positioned along the south-front of Fortress Holland. The one assigned to Group Kil (near the important Moerdijk bridges) would be in action for four consecutive days and be the main artillery unit responsible for pounding the German occupied Willemsdorp and Moerdijk bridgehead. Tragically enough it seems that they killed and wounded more Dutch than German troops. Particularly on the first day the batteries took aim at the former Dutch camp near the Moerdijk bridges, where the Germans had stowed the Dutch POW's. Also a barrage of the bridge entrance - supposingly on marching German troops - in fact lay on a column of Dutch POW's. The Germans felt some nuisance from the Dutch barrages but soon lived to learn with the occasional shelling from the slowly firing Dutch artillery mastodons.
The Germans captured most of the Dutch vintage guns too. Besides featuring as 'battlefield rarities' in the occasional German photo series, most guns shall have found a one-way ticket to German melting ovens to be transformed into modern means of war. One or two were saved from the oven and made it into Dutch museums.
