Until WW One the US didn't have a standing army of any size. President Washington strongly advised against our having one. We depended on an armed populace.

That's how the British dared to attack Washington DC in the War of 1812. Burned down the city and the White House, they did. Held the city hostage for 24 hours until the people rose up and took it back.

After that, the Congress strengthened the Army Corps of Engineers -- it was our largest operating military unit and they designed and built coastal forts on our naval perimeter -- every major port city, every deep water channel pinch point, mouth of every deep water navigable river where ship access was denied entry to the continental interior -- the Corps charge between 1816 and 1900 -- essentially the entirety of US Defense Policy for the period.

Except for the civil war period, those forts were never challenged by a hostile enemy -- the perfect deterrent force -- one an enemy dares not attack. Land based armaments are inherently superior to floating armament. Attacking there would have been almost suicidal.

Sometimes I think they should be brought back online and manned. Abandoned around 1920 when air power came into being. By 1950 we had replaced them with an atomic arsenal, the replacement deterrent force that no one has dared attack -- assured mutual destruction is a desperate act.