**The** word for the military action of shooting several targets at once
Solution 1:
In this video, the words simultaneous and synchronized shots are used. However, I believe the correct term is Simultaneous Engagement, as seen here quoted from the book Advanced Sniper Markmanship, which I believe was written by an instructor in this field.
Simultaneous Engagements
In certain situations, it's useful for several snipers to simultaneously engage the same target or multiple targets...
Solution 2:
Perhaps it was time on target, defined by Merriam Webster as
A concentration of artillery fire on a target in which the time of firing by each unit participating is so regulated that all the projectiles reach the target simultaneously
Solution 3:
A sniper's shot that kills more than one target is called a Quigley.
The term comes from the 1990 film Quigley Down Under, in which the eponymous character dispatches multiple opponents with a single shot
This newspaper article, and this one refers to the term.