Plain English Meaning

Three nautical miles — a measurement of distance used in aviation and at sea. A nautical mile is slightly longer than a regular mile. So 3 NM is roughly 3.45 regular miles, or about 5.6 kilometers.

Full Definition

A distance of three nautical miles, where one nautical mile equals 6,076 feet (approximately 1.15 statute miles or 1,852 meters). In the context of warning areas, 3 NM refers to the distance offshore from the U.S. coast at which a warning area begins, marking the boundary beyond which the airspace lies in international waters.

Context Anchor

Seen in special use airspace descriptions, especially when learning where warning areas are located relative to the U.S. coastline.

Derivation

Nautical mile comes from the Latin nauticus, meaning 'of ships,' because this unit was developed for sea navigation. It is based on the Earth's geometry — one nautical mile equals one minute of latitude — which is why both pilots and mariners use it.