In the Age of Sail, and in general before the end of World War II, gunboats were slow, weakly armored, and did not have the set of powerful weapons that main surface combatants had. For defending gunboats, like the Dutch ones were, this put a minimum requirement on the range of their guns. These weapons had to match the range of the weapons of the opponents that could appear in the area. Otherwise, opposing main fleet units could simply destroy the defending gunboats from a safe range, before attacking the shore.
The Dutch started to construct an armored fleet from 1865. They then opted to use the 23 cm Armstrong rifled muzzle loading gun as its main weapon. It was thought to be the minimum size for a gun that would be able to penetrate the armor of most opponents. In turn this minimum size would allow the Dutch ships to easily retain the shallow draught that was necessary in their home waters.
In about 1875, the Dutch government concluded that the 23 cm Armstrong RML could no longer match the main guns of the fleets of their possible opponents.[6] The Dutch started to look for a replacement, and found the 28 cm A No. 1 gun. This was a Krupp Breechloader of 28 cm and 22 calibers long. It was by all means superior to the 23 cm Armstrong RML. The Dutch government then decided that the 28 cm A No. 1 gun would become the standard heavy weapon of the Dutch fleet in the home waters.
New gunboats
The preceding Ever class
In 1873 the first two gunboats of the Ever class. HNLMS Ever and HNLMS Hydra, had been commissioned. The Ever class had been modeled entirely on mounting the 23 cm Armstrong RML. As a consequence many ships of the Ever class were commissioned while they were already obsolete.
The design of the Wodan class
The Dutch authorities had been very satisfied with the preceding Ever class.[7] When they realized that the days of the 23 cm RML were over, they therefore decided to make a new series of gunboats modelled on mounting the 28 cm A No. 1 gun. This decision was taken in a departmental order of 19 July 1876.[7]
Characteristics
General
The Ever class had been modeled on the British gunboat Staunch. The requirement to mount the 28 cm A No. 1 gun instead of the 23 cm RML, led to only a slight enlargement of the Ever design. I.e. from 196 ton displacement to 245 tons, that is only 25% larger. (cf. the difference in weight of 12,700 kg for the 23 cm RML and 27,650 kg for the 28 cm gun, as well the difference in carriage weight) It sounds too good to be true, and it probably was.
Propulsion
Each ship of the Wodan class had two compound engines with vertical cylinders. There were two boilers that each had its own fire. The nominal power of each boiler was 15 hp. There were two screws, a requirement for good maneuverability in small spaces.[8] After the first boats: Wodan, Thor, Freijr, Njord, Tyr and Braga had been delivered, experiments with the propeller took place. The Tideman model propeller gave the highest speed of 7.5 kn, and was therefore adapted.[9]
The problem of simply enlarging the Ever to mount a bigger gun, was in the machinery. Except for a small change in cylinder diameter, this remained the same. The designed trial speed of Wodan vs Ever was 7.55 kn vs. 7.9 kn,[4] so only 0.35 knots slower. A subsequent overview of the speed of both classes, shows that the Wodan class was indeed only 0.4 knots slower during trials.[5]
15 cm No. 2 gun on Njord.
Armament
The Wodan class was originally armed with the 28 cm A No. 1 gun. This was a L/22 gun, meaning its length was 22 times its caliber of 279 mm. As shown above, the selection of the 28 cm L/22 gun was the reason to design the Wodan class. The 28 cm L/2 gun weighed 27,500 kg. Its carriage and sled amounted to 11,000 kg.[10]
Incredibly, many boats of the Wodan class would later lose their 28 cm A No. 1 gun. It would be replaced by the even heavier 28 cm A No. 2 gun of 30 calibers (L/30). In 1882-1883 the monitors Bloedhond and Wesp exchanged their twin guns 23 cm guns for a single 28 cm A No. 1 gun taken from Wodan class gunboats. Instead these Wodan's received new L/30 guns.[11] As the value of the monitors was higher than that of the gunboats, this exchange can only be explained by assuming that the monitors could not mount the longer and heavier 28 cm A No. 2.
The ships of the class lost their heavy 28 cm gun when it became obsolete. By the end of World War I all boats had been re-armed with guns ranging from 3.7 cm guns to the 15 cm No. 2 (Njord).[12] Many would grow old in all kinds of different roles. On the eve of World War II, some, like Freyr, were still serving
Royal Netherlands Navy