In the dark days following World War II, two enterprising brothers are torn apart by dark, sinister forces and made bitter enemies as they emerge from the wreckage of their PBM in the Bermuda Triangle.

A PBM was a plane/boat that could bomb -- used in WWII and afterwards.

I probably wouldn't use the word "dark" twice.

What is a PBM?

And what exactly are the dark sinister forces that makes the brothers bitter enemies?

And what becomes their objective goal as a result? ? What's the plot? ?It's not enough to set up a dramatic situation; a logline must also lay out a plot the follows as a result of the dramatic situation.