Liberty Defense Perimeter

The Liberty Defense Perimeter (LDP) is a boundary line that serves as the main part of the United States Department of War's plan for defending America against the Chimera. In the event of an alien invasion, the area within the LDP will serve as a sanctuary for humanity while the perimeter itself will be fortified with Liberty Defense Towers. Final fortification of the line was completed in July, 1952.

History
The idea was first mentioned in an analysis of enemy battle tactics. Discussing hypothetical invasion scenarios, the document notes that while an attack from the coasts or from Alaska would overwhelm any resistance, an attack from the northeast would allow for the creation of a heavily armed "Liberty Zone" in the southern United States and lead to a stalemate. It appears that the government used the Liberty Zone concept as inspiration for the LDP project.

Evacuation Plan
Once the mathematically inevitable invasion of America begins, the government will be moved inside the LDP specifically Denver, Colorado as the temporary capital, followed shortly thereafter by essential personnel, House and Senate members, and priority personnel, as well as any immediate family members they may have. They will be followed by military forces assigned to guard the zone. Once they have arrived, civil authority will allow for some groups of civilians to enter the area.

Defense
A War Department memo (LDP227489WK) describes the Liberty Defense Tower program, which consists of a series of 1,400 foot tall towers placed every 50 feet along the LDP. This comes to 38,780 towers along the whole of the Perimeter. The towers are armed with concussion shells that can fire at targets up to 50 miles away. President Grace approved construction of the buildings, and they were completed in September, 1951.

Breach
After SRPA forces failed to deactivate the Holar Tower in Iceland, Chimeran forces were able to destroy the Liberty towers defending the perimeter, allowing the safe zone to be vulnerable. On May 28th, 1953 the Liberty Defense Perimeter was then breached by the Chimera and roughly 63 million people were killed when the Chimeran Fleet blanketed the area with Spire missiles. The U.S. military, however, managed to hold the last remaining protection camp in Baton Rouge, Louisiana. During the fighting the Chimera must have sustained massive casualties to both ground forces, and the air fleet. The attack on the LDP most likely started with waves and waves of Hybrids and Grims rushing the soldiers defending the towers. Though they must have sustained massive casualties that they most likely succeeded. But saying since there were only eighteen Chimera airships at the time of Operation: Black Eden, the fleet also most likely took massive casualties and losses.