Hello Kurt,

In one of the books of the Helmsman series by Bill Baldwin there is a planet that has a number of  very ancient orbital forts with some sort of energy weapons that apparently has no power source. The story goes that sometime in the dim past these forts where able to save the planet. There is a very large facility that teaches in a religious way how to maintain and operate the forts. The main character Wilf Ansor Brim and friends are on the planet when an invasion begins. Through deductions they learn that the facility is actually a huge missile that is targeted on the system's sun. When the structure hits the sun the energy from resultant flares are guided down a channel that powers the weapons.

The books are, in my opinion, based on the end WW I, the post war years leading up to WW II. Overall a nice read.

Tom Rux