'Seatrain' was the Allied unrealised reciprocal of 'Sealion', namely a contingency plan for the evacuation of Major General Ernest J. Dawley’s US VI Corps from the southern sector of the 'Avalanche' beach-head at Salerno for rapid movement to reinforce Lieutenant General Sir Richard McCreery’s British X Corps in the northern sector of the beach-head (13/15 September 1943).

The somewhat panicked reasoning of Lieutenant General Mark W. Clark and the staff of his US 5^th Army was the same as that for 'Sealion', despite the objections of the naval planners that any such move would mean the loss of all the supplies landed with the corps that was to be moved, but the plan was scotched by General the Hon. Sir Harold Alexander, commanding the Allied 15^th Army Group, who arrived to take personal note of the situation on 15 September and agreed with McCreery that the concept was both unnecessary and very dangerous.