The Adder-class monitors were a group of six ironclad monitors built for the Royal Netherlands Navy in the 1870s.

There were some small differences, but the main difference was that the Adder class got a ram, which was very popular after the Battle of Lissa.

Haai would become the first monitor to be built by a private Dutch shipyard.

Just like the preceding Heiligerlee class, the Adders were armed with two 23 cm Armstrong rifled muzzle loaders.

[1] Later all ships of the class were re-armed with the 28 cm A No.