From Conrad's Wiki
Classis Umbra – The Shadow Navy
Note: Surely they wouldn't be using Latin, but I haven't come up with another name yet. Other than Shadow Navy or Shadow Fleet, of course.
Classis Umbra is the elite exploration force of a magic-rich empire. From heavily guarded bases, these enchanted vessels “sail” from their homeworld into the Plane of Shadow and hence to the material realm upon a thousand different worlds. Merchants, ambassadors, spies, and missionaries depend upon the shadow navy to deliver them to the colonies, allies, and enemy powers of an empire that touches many worlds.
The magical technology behind this is powerful, but simple. Each of the enchanted vessels is a large flat-bottomed barge constructed of dark wood, and empowered to briefly encompass the entire vessel with shadow and then to shadow walk with its entire crew. This power can only be used once per day, but this is sufficient to allow crews to travel to other planes and other worlds.
In the material plane, these barges behave as normal, floating on water, or sitting static on the ground. When they enter the Plane of Shadow, they may “sail” at speeds appropriate to that spell.
To activate its shadow walk power, a shadow vessel must be covered in shadow. By design it creates an aura of shadow (dim light conditions) around itself when the activation is attempted. However, this aura of shadow can be countered or dispelled by a darkness or light spell. Such an event ruins the activation effort for the day, and the shadow vessel may not activate again until the next day.
The transit technique used by Classis Umbra requires a dangerous passage through the Plane of Shadow. In order to travel the incredible distances to other worlds, the crew must pilot the ship away from the material plane to the edge of some other plane, and then pilot the ship back to the material plane but towards some far destination. Each leg of this journey takes 1-4 hours. The treacherous nature of the Plane of Shadow ensures that even when a navigator follows the specific shadow charts meticulously developed by the navy over time, the trip varies in length.
Barring disaster, this means that a trip to another world take 2-8 hours, spent traveling to the edge of another dimension and then to the targeted world in the material plane. The Plane of Shadow is inhabited by many fearsome creatures, however. It is the duty of the Shadow Navy to ensure that disaster does not come to their vessel and its passengers. Dangers ranging from shadow mastiffs, to undead, to terrifying dragons of shadow await an unwary crew.
The maps kept by the Shadowy Navy include only the heavily guarded bases of their own homeworld. They are acutely aware that one of their vessels could be seized, and its maps put to use. The opportunist who manages such a thing will face fierce resistance on the imperial end of the trip.
The members of the Shadow Navy travel to distance worlds, through a dangerous realm. Their officers are authorized to represent the will of the empire in many unexpected situations on remote worlds. Within the confines of naval code, the captain's word is law.
The Shadow Navy uniform is dark gray. Insignia for rank are typically small and composed of silver set with onyx or obsidian. Personnel are discouraged from wearing shades other than white, black, and gray. People who travel with, but are not part of the Shadow Navy often are unaware of, or choose to ignore, such dress code. Over time, this has led to slang terms such as peacocks, colors, and brights when referring to non-navy passengers.
One of the few guild unions to cross into multiple worlds, the Company of the Lightermen is composed of workers who transfer goods to and from Shadow Navy vessels. They also dominate civilian operations at Shadow Navy bases and embassies.