 In order to prevent Jewish illegal migrants reaching Palestine a naval blockade was established to stop boats carrying illegal migrants, and there was extensive intelligence gathering and diplomatic pressure on countries through which the migrants were passing or from whose ports the ships were coming.When an illegal immigrant ship was spotted, it would be approached by warships, and would often maneuver violently to avoid being boarded.British boarding parties consisting of Royal Marines and Paratroopers would then be sent to take control of the ship.