Navis Imperialis - Origins: The origins of the Imperial Navy lay in the campaigns of the Great Crusade that began in ca. 800.M30. The Great Crusade was the largest and most ambitious military endeavour ever undertaken by Mankind. As mighty and valiant as the hosts of the Emperor were, this epic undertaking would have been entirely impossible without the countless thousands of Warp-capable vessels that transported hundreds of thousands of the superhuman warriors of the Space Marine Legions and many millions of Imperial Army soldiers from one star's light to the next.The Great Crusade saw a staggering array of vessels constructed, reclaimed or pressed into service. Some were used for a matter of solar months before being declared obsolete or wearing out and degrading to destruction, quite apart from losses incurred in battle, while others gained a permanent place in the canon of war, with successful designs endlessly copied and modified as the decades progressed. The first vessels to enter the service of the Imperium were constructed in the orbital foundries of Terra, and later Mars' Ring of Iron and the orbital shipyards of Saturn, under the scrutiny of the Emperor and the Forge-wrights of the Mechanicum, and indeed it was only in alliance with Mars that the trans-solar expansion was possible in any meaningful way.This was further aided when at last the Saturnyne Dominion, with its accomplished ship-masters, joined the Imperium after their alien overlords were overthrown, and as the Imperium expanded, many more great shipyards were added: Voss, Grulgarod, Lorin and Cypra Mundi, all grew to near rival Mars itself in voidship production.Driven by the will of the Emperor, the first Expeditionary Fleets pushed outwards into the galaxy. Preceding each great Expeditionary Fleet of hundreds, sometimes thousands, of vessels often ranged smaller contingents of independent flotillas led by a class of martial leader that would become known as the Rogue Traders Militant. Many of these individuals were former rulers of the numerous realms the Emperor had cast down first during the Unification Wars and later, as the Great Crusade spread, came to include leaders of formerly independent human worlds.They were offered a stark choice--bend their knee before the Emperor and swear service to the Great Crusade, or die by His hand. Though many set pride before what they regarded as slavery, others chose service and took up the Emperor's Warrant of Trade. There was a price, however.The Rogue Traders Militant were expected to scout ahead of the leading edge of the Great Crusade, accompanied by their own armies as well as whatever assets had been ceded them by the Emperor. Operating so far ahead of the Emperor's crusading armies, the Rogue Traders Militant could expect little or no aid should they encounter foes too powerful for them to overcome.After several solar decades penetrating the inky black of the void, Rogue Trader Militant fleets often appeared as ramshackle vagabonds, many of their starships taken from defeated enemies, sometimes including xenos vessels of entirely novel or esoteric form. They were forbidden to return to Terra, for in His wisdom the Emperor sought not to just rid Himself of powerful rivals, but to ensure that even in their deaths they might serve Mankind. Many vanished alone and unheralded; slain, consumed or enslaved by nameless xenos abominations far from the light of Terra.As the Imperium expanded, so too did its fleets. Countless long-lost wonders of technology were recovered, some wrested from the dead hands of unwilling custodians, and others surrendered willingly as fitting tribute to the Master of Mankind. Some vessels were unique, constructed by methods even the most accomplished Adepts of Mars could not hope to replicate: the Terminus Est, the Nicor, the Mirabilis and the Phalanx foremost among them. Other patterns and classes proved possible to reproduce and replicate, and before long the various arms of the Imperium's military acquired their own distinctive panoply of warships.Those of the Legiones Astartes were often blunt of prow and slab-armoured, built to endure the withering storm of fire that accompanies a planetary invasion, their plasma furnace-hearts powering some of the most destructive weapons known to Mankind. But beyond these practical needs, each fleet favoured the nature of its Legion, from the sable black marauders of the Raven Guard to the baroque crimson and gold battlecruisers of the Blood Angels to the brute functionality and unadorned steel of the Iron Warriors' siege-barques.The ships of the Emperor's wider naval armadas were more diverse affairs, built for void supremacy. They ranged from stately battleships, multi-kilometre long engines of doom, their armour concentrated to the fore and their flanks repleted with rank upon rank of broadside batteries, to lithe and deadly destroyers and stripped-bare Warp Runners, to watchful piquet frigates and lumbering star-fortresses. Beyond these were innumerable classes of transports, arks, conveyers and supply ships, the forge vessels of the Mechanicum and their own strange space-going engines of war.