Jack是海军用语，指悬挂在舰首的旗帜。英国军舰舰首都是挂国旗，因而得名。英国国旗除了叫The Union Flag之外，还有一个The Union Jack的别名。
Sailors used to speak of a “Jack” when they meant a flag which was set near the bow of a sailing ship.The flag showed the country to which the ship belonged.The Union Jack became the flag of Great Britain.Australia's flag has the Union Jack in the top left hand corner together with the stars of the Southern Cross.They have kept this small part of Britain on their flag because their country was first settled by people from Britain.
Australia's flag is the same color as the Union Jack—red，white and blue.The act of joining together is called a “Union”．The Union Jack was the name of the flag made when England，Scotland and Ireland joined together to make one country.It all began in 1707 when England and Scotland joined together to become one nation.A flag was made using two crosses—one for the patron saint of each country.The word “patron” means “protector”．Many centuries before the English had taken St George as their patron saint，his emblem was a red cross on a white background.
The Scottish patron saint was St Andrew.In memory of him，they used a white cross on a blue background.This cross was shaped like the letter “X”．The new flag was a mixture of both flags with two sets of crosses.When Ireland joined England and Scotland in 1800，another cross was added.St Patrick's cross of Ireland was red and also shaped like an “X”．All three flags made up the Union Jack.
