Mahan contrasts an eastern power guarding extended communications with Britain operating from a central position. British forces can choose which end of that extended front to threaten. He compares the English Channel and Irish Sea with the Mediterranean's position between the Atlantic and Indian Ocean, and the northern Scottish route with the voyage around the Cape of Good Hope. The scale differs, but each comparison concerns the cost of a detour around an opponent's position. He then connects Britain's naval commitments to its inability to afford an army as large as those of continental powers. Protection against invasion therefore depends on the fleet. Command of the sea serves both the offensive requirement to defeat the enemy's organized naval force and the defensive need to secure Britain.
Notable Point · 1:16:30-1:18:34
Interior lines and Britain's dependence on the fleet
Mahan uses geographic analogies to explain Britain's central position, then connects its imperial naval commitments and smaller army to dependence on command of the sea.