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Enfilade and defilade are concepts in military tactics used to describe a military formation's exposure to enemy fire. In addition, enfilade fire is used to describe gunfire directed against an "enfiladed" formation or position. The words themselves come from French (enfiler - to skewer; défiler - to scroll).

Enfilade fire is also commonly known in English as "flanking fire".

A German bunker on Juno Beach Top: Wounded Canadian soldiers, 6 June, 1944. Middle: The same bunker in September, 2006. Bottom: The view from the bunker, showing the enfilading field of fire with respect to the seawall.

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 (flank).

The benefit of enfilading an enemy formation is that, by firing along the long axis, it is relatively easier to hit individual troops within that formation. Raising or lowering the aim of the firing weapon merely directs the fire to a different point along the axis of the formation, though any pivoting movement (traverse) of the weapon is more likely to result in a miss. Enfilade fire takes advantage of the fact that aiming at a target is relatively easier than correctly estimating the range to avoid shooting too long or short. Finally, projectiles that miss an intended target are more likely to hit a different target within the formation if firing along the long axis.

The picture to the right illustrates the concept of enfilading fire well. This German bunker was built on a bulge in the sea wall which sticks out well into the beach; any troops sheltering behind the sea wall would still have been completely exposed to fire from this gun position, and would have been neatly lined up along the gun's axis of fire. Thus troops hiding along the sea wall would have been enfiladed by this gun.

Raking fire is the equivalent term in naval warfare.

Strafing, firing on targets from a flying platform, is often done by enfilade fire when using forward weapons, and defilade fire when using side-mounted weapons.

A unit or position is "in defilade" if it is protected from direct exposure to enemy fire. For an armored fighting vehicle (AFV), defilade is synonymous with a hull-down or turret-down position.

Defilade is also used to refer to a position on the reverse slope of a hill or within a depression in level or rolling terrain. Defiladed positions on hilltops are advantageous because they allow a defender to take advantage of the height of the terrain without suffering the disadvantage of being silhouetted against the sky. However, because of the slope, "dead space" that cannot be engaged with direct fire will be created in front of the position. Ideally this dead space should be covered by the interlocking fields of fire of other nearby positions, and/or by pre-planned indirect fire such as mortars or other forms of artillery.

In the case of antitank weapons, and especially short-range man-portable antitank rockets, defiladed positions behind a hill have several important advantages. This is because the dead space created by the intervening crest of the hill prevents an approaching tank from using the range of its direct-fire weapons, and neither the attacker nor defender will have a clear shot until the tank is within range of the defending antitank weapon. In such engagements the tank is usually at a further disadvantage because the defender will often be camouflaged while the attacking tank will be silhouetted against the sky, giving the defender an easier shot.

In addition, if the tank fails to detect the defending antitank weapon while the tank is still defiladed, but advances beyond that position to the crest of the hill, it may expose the relatively thinner armor of its lower hull or belly to the defender. Early detection and elimination of antitank threats is an important reason that tanks attack with infantry support.

Artificial entrenchments can provide defilade by allowing troops to seek shelter behind a raised berm that increases the effective height of the ground, within an excavation that allows the troops to shelter below the surface of the ground or a combination of the two. The same principles apply to fighting positions for artillery and armored fighting vehicles as well.

• Russian Fortresses, 1480–1682, Osprey Publishing, ISBN 1-84176-916-9
• René Chartrand, French Fortresses in North America 1535–1763: Québec, Montréal, Louisbourg and New Orleans (Fortress 27); Osprey Publishing, March 20 2005. ISBN 9781841767147

• Raking fire
• Crossing the T
• Reverse slope defence