Spycraft and submersibles - our two hapless cavalrymen have their work cut out for them!

Even as the sea blockade by the Union Navy slowly strangles the South, the picket ships begin to mysteriously blow up one after another. Lincoln, worried that the war could stretch on too long if the Rebels are resupplied, orders that the Confederates' secret weapon be identified. That means sending spies to Charleston, though, in the heart of the enemy's territory. And who will be the two unlucky fools the brass entrusts with such a dangerous mission … ?