The Zeelandian Navy had the two Isengard class battlecruisers under construction to offset the Japanese Kongo and Kanto class battlecruisers. They were a fine design and would prove useful in the role of cruiser killers. But... they would not be able to stand against even the older Japanese battleships of the Hyuga (12x14") type or the even larger Nagato type (8x16"). Something bigger with better teeth and armour was required.
Laid down in 1937 and 1938, the Oceania class added two ships of better capabilities than the battlecruisers under construction. The Oceania was given high priority of double shifts, on the outbreak of the Second World War, so that it would be completed in early 1941, at least 6 months ahead of schedule. The second ship, Zeelandia, had its production stopped while priorities were sorted out. In July of 1940 the Zealandia was repurposed as an aircraft carrier. Construction being restarted with the new plans being drawn up.
The removal of the 13" armoured belt gave a large head start for the weight needed to fit the flight deck and hangar above the main deck. The ship had a large reserve of buoyancy and was able to make the hangar with twenty feet of headroom. This allowed all of the larger aircraft of 1943 forward to be able to be operated from the ship.
The Zeelandian Navy was able to put a Taskforce together with the five aircraft carriers and three modern battleships of its fleet being the core units. The Taskforce operated on the fringes of the main battles as coverage to stop any outflanking maneuvers by Axis forces. Its finest hour was when the fleet sank three aircraft carriers, one battlecruiser, two cruisers and a destroyer in one day. The Taskforce had been used as the cleanup force after the battle of Cape Engano and been tasked with sinking the cripples.
Both ships survived the war, the Oceania being used as fleet flagship. The Oceania was surveyed to have the aft end converted to carry missiles but it was decided that two of the cruisers would be converted instead. Oceania was kept as a bombardment unit and was used in this role at Korea and Vietnam. 1980 and the Oceania was removed from service and scrapped. The Zeelandia was converted twice to improve its capabilities. First time in 1954-57 was to install the angled deck and other landing on improvements to hand. Second conversion work made the ship better able to operate Sea Harrier aircraft.
The Zeelandia operated off Korea with the Allied forces, and off Vietnam with the US forces, and its final battles were around the Falkland Islands in 1982. Hit by three Exocet missiles, the Zeelandia was on fire for two days. The ship was completely burnt out and had to be abandoned and the hulk sunk by friendly forces.
