Jack a flag hoisted at the bow of a ship. In navies this is, as a rule, a flag identifying nationality, but not necessarily in the same design as the ensign, while on non-naval vesels, the jack may have other meanings, or be decorative. Length the maximum length of a flag, measured straight from hoist to fly. Merchant flag is a flag flown by a merchant ship. The rules of heraldry forbid placing color on color, or metal on metal.
National flag is a flag of a country.
Custom ordains that the length of the pennant should equal the length of the ship if she leaves her station at the end of a normal period of foreign service. It is similar to, and flown in place of, the masthead pennant, and is displayed by a ship from a foreign station when entering or leaving harbors during her passage home, and by a ship of the Home Fleet on leaving for and arriving at her home port. Admiralty Seamanship Manual 1951. A hydrogen balloon was sometimes attached to the end of the pennant to keep it flying. It is not always easy to distinguish a pennant from a flag.