A postman-turned-protester delivering letters flew a single-person gyroscope undetected through the nation's most secure and highly monitored airspace Tuesday, landing his aircraft yards from the U.S. Capitol before he was arrested.

His public declaration of intent to protest notwithstanding, how did he get through the expensive and lethal military assets that protect Washington, D.C.?

Most Washingtonians are vaguely aware that the region lies beneath a 24/7 canopy of combat air patrols. When passenger planes take off to the north from Reagan National Airport, they turn sharply left just after take-off in order to avoid crossing into airspace around the White House and near the U.S. Capitol. And since 9/11, under the mission name of Operation Noble Eagle, F-16 fighters and Coast Guard helicopters regularly chase small planes, usually general aviation aircraft, out of the larger Air Defense Identification Zone, which stretches out 30 miles from the center of Washington, D.C. The White House, the Pentagon, Capitol Hill, the CIA, and other military reservations were also fortified after 9/11 with air defense systems. More than 10 years later, the National Capital Region Integrated Air Defense System is touted as a model for protecting critical infrastructure, major cities, and military installations.

The NCR-IAD's warning equipment include visual warning lasers, flare cannons, FAA radars, military radar systems, advanced electro-optical sensors (Enhanced Regional Situation Awareness), and regular cameras.

Its "engagement assets" include the Norwegian Advanced Surface to Air Missile System (NASAMS) for long-range air defense; SLAMRAMMs — Surface Launched Advanced Medium Range Air to Air Missile batteries mounted on Humvees — for protection closer in; Sentinel phased array warning radar, which detects smaller targets at a range of 75 miles; and the Army's Avenger system for threats closer to the ground or closer to the center of the protected area. The Stinger missiles around D.C. require humans to air them and confirm targeting; they have a range of about five miles and can reach about 10,000 feet in the air.

The system is redundant. And it feeds a lot of information back where humans and computers decide whether blips and tracks represent commercial aircraft that are clean and cleared for the ADIZ by the FAA, or general aviation aircraft that might fly near the perimeter of the ADIZ, or even large flocks of birds, blimps — and yes — gyroscopes, friendly or hostile.

A confusing patchwork of operational orders, command relationships, and formal agreements govern how the air defense system is maintained. A set of classified rules are in place to allow the president, the secretary of defense, or delegated officers to decide whether to engage, i.e. shoot down, a target. Here is how the system is supposed to work.

NORAD/NORTHCOM Concept of Operations Plan 3310 puts the secretary of defense in charge of the entire enterprise. The commander of NORAD maintains operational control of the forces, along with a deputy responsible for direct command and control. That deputy and his battlestaff sit at Tyndall Air Force Base in Florida. From there, the forces diverge.

The integrated system of radars, missile batteries is operated by the Joint Air Defense Operations Center (JADOC) at Bolling, AFB. It is responsible for direct control of the missile batteries, defensive systems, and their sensors. Elements of the U.S. Air Force and U.S. Army staff the JADOC 24/7. For the fixed wing and rotary wing aircraft, including F-16s on alert at Andrew Air Force Base, command and control flows from the battlestaff at Tyndal to the Eastern Air Defense Sector in Rome, New York, which has direct tasking control over the aircraft, coordinates with the JADOC, fuses intelligence from NORAD, the FAA and other sources, and oversees the airspace itself.

A coordination center staffed by liaison officers from the Secret Service, Capitol Police, FBI, and other agencies receive the same information — a common operating picture — that the JADOC and EADS get, and add their own paint to the mix, also being asked with direct reach-back. (The Secret Service liaison officer would be in direct contact with various Secret Service command centers, for example). An unclassified and perennially active conference call, the Domestic Events Network, or DEN, is one of several ways that all of these entities coordinate with each other.

CNN reported that NORAD did not detect the gyrocopter. That's scarier, in most respects, than if they had detected it, and commanders had made a decision not to shoot it down.