Britain, like other colonial powers, established, controlled and accessed her empire from the seas. armed ships able to operate in shallow coastal and river waters. steam-powered screw or paddle driven vessel, sufficiently fast and manoeuvrable to take the enemy, whether on shore or afloat, by surprise. action, ranging from the Burma war in 1824, through two world wars and on to the dramatic escape of the Amethyst down the Yangtze in 1949.