Flash Towers formed a visual as well a RADAR ring around Saigon. Their purpose was to watch for flashes from artillery, rockets, gunfire, etc., plot the direction from the tower and pass the information over to the Tactical Operations Centre (TOC) at C.M.A.C. Hopefully another tower saw the flash and given the two plots through triangulation the TOC should be able to identify just where the flash originated and deploy a response by the use of artillery or air gunships. See TOC images for more information.

Flash Tower posts were either on the top of water towers, generally out in the country as shown in the picture on the left. That's me climbing up the ladder. Or, they were located on top of all buildings in the city as shown in the picture on the right. Note that the post on the top of the building is equipped with RADAR See domed antenna located to the left of the observation post. Not all posts had RADAR as the antenna needed to be several feet from the troops as protection from its effects. Source: Finnegan

The observation posts were generally manned with two personnel, 24 hours a day. When a flash or other incident is sighted the direction is identified by using a sighting board (see picture on the left) In the picture in the middle a soldier is using range finding glasses to estimate the range. In the picture on  the right the other soldier calls in the direction and range to the C.M.A.C. Tactical Operations Centre (TOC) for deployment.  Source: National Archives

This  view of the Counter Mortar RADAR equipment in operation around Saigon in 1969. Source: National Archives

The screen by today's standards was small.

Once a missile trail was identified,

Positioning the reference was done manually,

and the location was called into the TOC.

Pictures from J.W. Nugent. Lest to right: French water tower, Sublet to ARVN Unit, Vo Ho middle, kneeling.