Sonar Buoy (CTP1)

is a tile improvement in Civilization: Call to Power.
==Gameplay==
Sonar Buoys use sonar to detect units in proximity. Each Sonar Buoy has a vision range of 1 and can spot s. Sonar Buoys cost 150 PW and take two turns to build.
==Great Library entry==
In the 1930's the Allied Anti-Submarine Detection Committee invented a method of interpreting an echo generated by a burst of energy reflecting off of a naval target. The Americans named the technique "sonar" after its acronym sound navigation and ranging. Sonar could identify the range, speed, distance, and direction of both surface vessels and submarines. Sonar buoys remained hidden from the enemy though they allowed military intelligence to remotely gather information about the enemy's naval activities.