In the 1700s, the rattlesnake was a symbol of resistance to British oppression, because while it gives a fearsome strike, the rattlesnake always warns its would-be attacker in advance that it was willing to fight.
In 1775, the Continental Army largely adopted the popular Gadsden Flag design of a coiled rattlesnake that is still famous today. The Continental Navy followed suit. However, in the Naval version, the rattlesnake is extended in the midst of striking.
The First Union Jack or Navy Jack featured on this shirt has been changed many times over the years, but is still used by the U.S. Navy in it's original form on special occasions and for certain ships bestowed with the honor.
It remains a reminder that while we are a fair people who are not interested in engaging in conflict, we are not afraid of it either, and will fight with fervor to defend our rights and our way of life.