When boarding a military ship it is customary to salute the ensign then the Officer of the Deck (OOD) and request permission to come aboard. So why do they call it an ensign?
An ensign is a distinguishing flag of a ship or military unit. In todays military our ensign is the flag of the United States. In the early days the rank of ensign was given to the junior officer once responsible for bearing the ensign of his unit.
In nautical use, an ensign in the form of a flag is usually flown at the stern of a ship or boat to indicate its nationality. Ensigns may also be flown from the yardarm (on the ships main mast) of a ship underway, where it is known as a steaming ensign.
In port or at anchor the ensign is flown from the flagstaff at the stern of the ship. At the bow the union jack is flown from the jack staff. When the ship gets underway the flags are struck fore and aft while the ensign is raised on the mast.
Traditionally the union jack was a blue banner with 50 white stars. You will notice that LST 325 flies the First Navy Jack. This flag has the 13 red and white stripes with the timber rattle snake on it with the words dont tread on me
This flag was used during our struggle against the British in 1775. The timber rattlesnake is especially significant and symbolic to the American Revolution. The rattle has 13 layers signifying the 13 colonies and the snake does not strike unless provoked, thus the phrase dont tread (step) on me.
In later years this flag was flown by the most senior ship of the navy but in May of 2002 the Secretary of the Navy authorized ships to fly the flag in response to the terrorist attacks of September 11, 2001.