Portsmouth's existing seaward defenses made a direct naval assault unlikely. An attacker could instead land troops nearby and raid the naval base from inland. Steamships increased that concern because an expedition could arrive with less dependence on favorable wind and tide. The landward Palmerston forts addressed this route of attack, even though their orientation surprised people expecting every coastal defense to face the sea.
Notable Point · 28:49-29:48
Steam-powered raids made Portsmouth's landward defenses necessary
Strong seaward defenses encouraged an attacker to approach Portsmouth overland, while steamships made a sudden raid less dependent on wind and tide.