The Reichsmarine of the Imperial 4th Reich, more commonly referred to as the Imperial Reichsmarine or the Imperial Navy was the maritime military force of the 4th Reich. It existed for a short period of time, primarily inheriting ships and vessels from the United Federation Navy, changing certain ship's names, but keeping most of them. It held the prefix ISS, for "Imperial Sailing Ship."
The Reichsmarine only existed for the majority of the Third Great Prairie War, and it's primary goal in that conflict was to facilitate resupply and conquest for the Imperial Army. Madden was not a so-called "Navy Man," as a majority of the Federation's presidents had been, and so did not have a great understanding for naval tactics. Anderson, while having a distinguished naval career, did not involve himself strongly in naval matters during the war, or many matters outside of strategic bombing and nuclear warfare, so the Reichsmarine was in large part undirected daily throughout the war.
However, it did have clear objectives. At the opening of the war, the primary aim of the Reichsmarine was to destroy what Madden (correctly, history would prove) to be the most capable opponent it faced, the nascent United Manonan Navy. At the start of hostilities, the Imperial Reichsmarine outnumbered every other navy in the SPN combined, and even further outstripped their projected capabilities.
In comparison to the United Manonan Navy, the Reichsmarine boasted:
9 Supercarriers
10 Light Carriers / Amphibious Assault Ships
2 Battleships
3 Heavy Cruisers
1 Light Cruiser
4 Missile Cruisers
7 Destroyers
1 Attack Submarine
9 Ballistic Missile Submarines
The Manonan Force consisted of:
8 Fleet Carriers
1 Battleship
1 Light Cruiser
2 Missile Cruisers
5 Destroyers
3 Attack Submarines
The first major engagement, however, would not occur until the 13th of December, 2021, by which time the Manonan Navy had added 4 more fleet carriers, another Battleship, and numerous other vessels, but still lacked the tonnage of the Imperial Navy when the Battle of Whitefish Bay saw the fleets lock horns for the first time. The Manonan Navy achieved an unlikely victory destroying two of the Imperial Submarines and severely damaging a supercarrier, though losing a fleet carrier in the process.
Over the course of the war, the Imperial Navy continued to fail in it's two stated objectives - "enable further conquest of the [so-called] illegitimate aggressors [the Allies]" and "The Destruction of the United Manonan Navy, the bulwark against our defense." These goals, from Madden himself, were already failing to be met before the Battle of the Dune Sea, sometimes called "Manona's Midway", and it had an almost identical effect on the Imperial Navy, inflicting heavy - in the economy of the Reich, irrecoverable - losses on the carrier fleet.