From the Imperial sourcebook."Stormtroopers are the Empire's calling card. Wherever the Empire goes, stormtroopers will be found, acting as ship's troops aboard Star Destroyers, accompanying visiting dignitaries to outlying worlds, and maintaining garrisons on trouble-torn worlds. Working in conjunction with the Imperial fleets, stormtroopers enforce the Emperor's will in an effective and brutal manner.
Unlike the Imperial Army, which is entirely geared toward ground operations, stormtroopers function equally well in space and on the ground. Trained to quickly seize ground installations during planetary assaults and to act as security troops on starships and battle stations, stormtroopers are far more flexible than regular army units.
As assault troops working in conjunction with Imperial Navy and Imperial Army armored units, stormtroopers are second to none. Their ability to rapidly overwhelm and capture enemy positions makes them the first choice for leading assaults on important worlds. Often stormtroopers are used to clear away the enemy's first line of defense and establish a ground base to allow the unopposed landing of transports carrying regular Army units. The Army, in these situations, is used to mop up resistance and maintain an Imperial presence.
Except in systems where prolonged struggles threaten to disrupt the Empire's industrial capacity or weaken its strategic positions, stormtroopers will be withdrawn once they have secured a landing zone. The complete subjugation of a world is left to the Imperial Army. Where a quick victory is essential, large numbers of stormtroopers will be deployed to crush the opposition as quickly as possible. On worlds where the Empire has established important military bases or research establishments, units of stormtroopers are used to stiffen regular Army units."
I was just wondering........ doesn't this just make the stormtroopers the Imperial equivalent of the Royal Marines? I mean, other than them having no organic armour support attached, they just fit so perfectly. They expect armoured support attached to them by the Army in the form of AT-AT and AT-ST, they have their own mobile vehicles in hoverbikes(our equivalent of Rovers?),they're primarily light infantry with their own infantry support like mortars and portable anti-air weapons.They rely heavily on aerial support provided by the Imperial navy, their mission roles include the traditional SOI, securing and establishing a base of operations, capturing enemy vessels(Tantive IV!) and they have attached to them specialised corps of troops for special missions.
Hell, naval security on board ships appear to be the domain of black helmeted naval troopers, the equivalent of naval RPs.