Enfilade
A formation or position is "in enfilade" if weapons fire can be directed along its longest axis. For instance, a trench is enfiladed if the opponent can fire down the length of the trench. A column of marching troops is enfiladed if fired on from the front or rear such that the projectiles travel the length of the column. A rank or line of advancing troops is enfiladed if fired on from the side (from the flank).
The original concept of enfilade fire is one for field artillery, where battery officers strive to place their weapons on an enemy's flank, firing down his battle or trench line and achieving greater effectiveness. Napoleon was a master at this. When naval formations "Cross the T" (see below), they have achieved the superior battle position of firing on the enemy along his long axis. The benefit of enfilading an enemy formation is that, by firing along the long axis, it becomes easier to hit targets within that formation. Enfilade fire takes advantage of the fact that it is usually easier to aim laterally (traversing the weapon) than to correctly estimate the range to avoid shooting too long or short. Additionally, both indirect and direct fire projectiles that might miss an intended target are more likely to hit another valuable target within the formation if firing along the long axis.
When planning field and other fortifications, it became common for mutually supporting positions to be arranged so that it became impossible to attack any one position without exposing oneself to enfilading fire from the others, this being found for example in the mutually supporting bastions of star forts, and the caponiers of later fortifications
Fire is delivered so that the long axis of the target coincides or nearly coincides with the long axis of the beaten zone.
Read more about this topic: Enfilade And Defilade