April 12: The Union Flag is adopted for the English and Scottish vessels in 1606.

The Union Jsck:The flag of the United Kindom 

On April 12, 1606, King James VI of Scotland and James I of the Personal of both states decreed the design of the flag union between England and Scotland so that ships could sail with the backing of the United Kingdom of Great Britain. That is the origin of the earlier flag of the United Kingdom of Great Britain and Northern Ireland today.

Saint George's Cross.

In 1194, Richard I of England introduced the cross of Saint George: a red cross on a white background as the national flag of England. At that time, England, Wales and Scotland were three separate kingdoms. But Henry VIII annexed to Wales in 1536. For that reason, when the union flag was proposed to be hoisted on English navy ships, Wales and England had been already built by English military conquest.

St Andrew's Cross
The Saltire

The cross of Saint Andrew of Scotland, has two diagonal white lines on a dark blue background. Saint Andrews was a Christian martyr and patron of Scotland who was crucified on an X-shaped cross. During the reign of William I, around 1180, the Scotish began to use the flag of blue background with a cross shaped white X and became in heraldic symbol popularly referred to as “The Saltire”.