The Battle of Kan (, Kan no eki), also known as the Second Battle of Hakata Bay, was the second attempt by the Mongol-led Yuan dynasty of China to invade Japan after their failed attempt seven years earlier at the Battle of Bun'ei. In the summer of 1281, the Yuan invaded with two large armies. The Japanese defenders were aided by a major storm which sank a sizeable portion of the Yuan fleets. The invaders who reached the shore were repulsed shortly after landing. The Japanese called the opportune storm kamikaze (lit.'divine wind'), a name later used in the Second World War for pilots who carried out aerial suicide attacks.

Major military efforts were taken by Kublai Khan of the Yuan dynasty in 1274 and 1281 to conquer the Japanese archipelago after the submission of the Korean kingdom of Goryeo to vassaldom. Ultimately a failure, the invasion attempts are of macro-historical importance because they set a limit on Mongol expansion and rank as nation-defining events in the history of Japan. The invasions are referred to in many works of fiction and are the earliest events for which the word kamikaze ("divine wind") is widely used, originating in reference to the two typhoons faced by the Yuan fleets.

The invasions were one of the earliest cases of gunpowder warfare outside of China. One of the most notable technological innovations during the war was the use of explosive, hand-thrown bombs.