This led Teller to suggest a "pop-up" mode where an Excalibur would be placed on SLBM platforms on submarines patrolling off the Soviet coastline. When a launch was detected, the missiles would be launched upward and then fire as they left the atmosphere. This plan also suffered from several problems. Most notable was the issue of timing; the Soviet missiles would be firing for only a few minutes, during which time the US had to detect the launch, order a counter-launch, and then wait for the missiles to climb to altitude.