In his televised statement Kennedy declared a naval blockade of Cuba. All incoming vessels would be searched before they would be allowed to proceed to the island nation. Some ships that had been approaching the quarantined area reversed course and headed back to Russia. Others were allowed to pass after being boarded and inspected.
It was a dangerous operation. Freighters jostled with US Navy ships. Soviet submarines were patrolling nearby. An inadvertent accident could escalate tensions. To buy time and reduce the risk of accident, Kennedy shrunk the size of the blockaded area. He wanted decision makers on both sides of the conflict to have more opportunity to weigh their alternatives.