Cruiser - Imperial Navy Cruisers: The conduct of the Great Crusade required vessels by the thousands, vessels that could not only carry armies and bring apocalyptic destruction to bear, but that could also endure the perilous transit of Warpspace and the titanic forces and hardships of the Empyrean and the deep void both.Military vessels were needed to replace losses and meet the ever expanding demands of the expeditionary fleets, the Imperial Army's Armada Imperialis and, on a lesser scale, the Rogue Traders and local star system defence navies. To satisfy this constant need, a bewildering variety of classes of warship were developed to fulfil an equally bewildering variety of tactical roles.Light cruisers and heavy cruisers are medium-sized Imperial warships, ranging in general terms between 4 and 6 kilometres in length and with an on-board complement of crew ranging into the tens of thousands. They are intended primarily for independent military operations such as raids, outpost assaults, deep-range patrols and search-and-destroy missions, and for use as "workhorse" warships in larger fleets and squadrons.The difference between the two primary types of cruisers is principally found not in general size (although this may also be the case) but role and tacical specialisation; heavy, or armoured cruisers as they are also known, are designed to favour defence and firepower (particularly over-gunned ships for their class may be referred to as battlecruisers).A noteworthy but relatively uncommon type of Imperial warship, grand cruisers are "pocket battleships" -- something of a halfway house between a battleship and a cruiser in size and firepower. They were intended principally to be capable of operating on their own rather than as part of a larger fleet, however, and are often further specially designed either for range (which was to say duration of deployment without significant resupply or refit) or to mount a specialised weapon system which required particular tactics to utilise. Grand cruisers make for formidable heavy raiders and could use their range and speed to catch targets unawares, as well as serving as powerful flagships for small fleets of cruisers and escorts.The galleass of war is an equivalent vessel to a grand cruiser (though often much larger physically), much of whose fabric is given over to freight and transport capacity, while still maintaining formidable armaments and defence. They make for ideal support vessels for deep-range explorations into unknown regions of space and were used in ancient times as the flagships of the most powerful Rogue Traders Militant.Light cruisers sacrifice some of the favoured elements of heavy cruisers for greatly increased speed and manoeuvrability. Both however are more than a match for any warship smaller than themselves, and will be the death of any civilian ship it chooses to turn its wrath on.Just as with battle barges -- but on a smaller scale -- strike cruisers are modified designs used by the original Legiones Astartes and their Successor Chapters of the Adeptus Astartes, optimised and reconfigured for planetary assault and voidship boarding actions in primacy over other roles.No cruiser of any type can hope to match a true battleship in an open fight on equal terms, and so in any "clash of the line" between fleets, they are used in a supporting role for their side's battleships and battle barges, their role primarily to use their speed to carry out flanking attacks, combine their firepower, and to harry and finish off wounded ships of the line.Because of the flexibility of their hulls and their relatively smaller scale in comparison to a battleship -- needing far less resources and material to construct as a mighty capital ship -- cruiser-sized hulls are also used for a wide variety of rarer variants and specialised functions.As a result, minor cruiser classes such as siege monitors, attack carriers, pursuit cruisers, arvelasters, torpedo rams, claw-cruisers and shield-barques can all be found in the ancient Armada Imperialis order of battle and as relics in the Space Marine Chapter fleets and Navis Imperialis of the 41st Millennium.