The John W Mackay was a ship in Venice, Italy in 1938. While fleeing from members of the Brotherhood of the Cruciform Sword in a motor boat, the driver Elsa Schneider, and Indiana Jones headed in the direction of the John W Mackay and another ship, the Tiber.
Preoccupied with fighting off the Brotherhood, Jones directed Elsa to not go between the ships. She misheard, however, and took the boat between them. One of the Brotherhood's boats followed and the archaeologists made it out through the other side as the gap between the Mackay and the Tiber began to close but the Brotherhood's vessel exploded in the impact.