signal flag displayed by a vessel about to leave port
Maritime flag Ensigns are usually required to be flown when entering and leaving harbour, when sailing through foreign waters, and when the ship is signalled to do so by a warship. Warships usually fly their ensigns between the morning colours ceremony and sunset when moored or at anchor, at all times when underway, and at all times when engaged in battleâ€”the "battle ensign". When engaged in battle a warship often flies multiple battle ensigns. This tradition dates from the era of sailing vessels. Tradition dictated that if a ship lowered its ensign it was deemed to have surrendered. Masts were targets of gunfire, and the second and subsequent ensigns were flown in order to keep the ensign flying even after a mast hit.