SECURITY Security consists of those measures that prevent surprise, avoid annoyance, preserve freedom of action, and deny to the enemy information about our forces. Security is not only keeping watch to detect the enemy but also deceiving the enemy as to the strength of the battalion, location of the weapons, and other valuable information. Using camouflage effectively is very important to security.

MUTUAL SUPPORT A well-developed defense plan includes mutual support from adjacent units. Seabee units are normally attached to an MAGTF and have a variety of mutual support. However, conditions, created by wide unit separation, increase the problem of achieving mutual support. Support of adjacent units by fire can be hampered by distances that exceed the ranges of the supporting units organic weapons and must be considered when seeking mutual support. Mutual support becomes critical when conducting a convoy. Normally the convoy will travel out of range from a Seabee unit's organic weapons, so mutual support from adjacent units becomes critical.

ALL-AROUND DEFENSE Although the platoon commander positions the squads toward the expected direction of an enemy attack the platoon must be prepared to defend against an attack from any direction. The possibility of multi-direction enemy attacks, including helicopterborne or airborne attack, increases the importance of this principle. All-around defense is best achieved by early warning and the rapid shifting of platoons into supplementary fighting positions to counter a developing attack. The topic of fighting positions is discussed further in this chapter. Early warning capability provided by air defense elements of the Marine Aircraft Wing (MAW) can provide defense against helicopterborne or airborne attacks.

IN-DEPTH DEFENSE Maximum defense in depth is required to absorb an enemy attack within the battle area. Defense in depth applies to the squad level by engaging the enemy at maximum small-arms range as it advances and continuing this fire until the enemy has been stopped. The requirement for depth is increased when the enemy is superior in mobility or has the capability of destroying or rupturing defensive positions by using nuclear weapons. Organized in-depth positions must control key terrain, block avenues of approach, reduce the defender's vulnerability to nuclear weapons, and assist the maneuver of the reserve troops.

COORDINATED FIRE PLAN Coordination of all fire from weapons organic and supporting the battalion is considered. Included in a coordinated fire plan is naval gunfire and tactical aviation support usually provided by the Marine Air Group (MAG). Coordination between the companies is also critical. The fire of the squad forces the enemy to slowdown and deploy, thus creating a target for the mortar crew of the battalion, adjacent companies, or supporting weapons. This makes the squads a key element in a coordinated fire plan.

COORDINATED BARRIER PLAN Using barriers, either natural or man-made, can channel, direct, restrict, or stop enemy movement. The effective use of barbed wire and concertina, claymore mines, antitank mines, and antipersonnel mines, and the effective use of the terrain add to the defense of the battalion. Natural obstacles must be exploited. The creation or exploitation of barriers must be coordinated at all echelons of the command.

FLEXIBILITY A platoon commander must continually develop various courses of action to meet the enemy threat. Being flexible is to ask yourself, What should I do if the enemy does this?

DISPERSION Normally in a defensive situation, squads are limited to how spread out they are over a wide area. Firing positions are assigned and should be close enough to provide interlocking fire. They should not be close enough so an enemy machine gun or mortar can wipe out an entire fire team or an entire squad. The degree of dispersion will be influenced primarily by the mission and by the following:

. Terrain . Friendly and enemy air situation l Mobility of opposing forces . Enemy nuclear capability . Responsiveness of friendly nuclear and conventional fire support

USE OF TIME AVAILABLE

Since the defender can examine the terrain in detail and plan its best use, every effort is made to prepare the defense in advance. The time available for planning and preparing for the defense will influence the following:

Tactical employment of the companies Preparation of obstacles Coordination of fire from each company Coordination of supporting fire Priority for performance of tasks The effectiveness of the defense depends not only on the time available for its planning and preparation but also on its advantageous use during the preparation phase. This fundamental also applies after the preparation phase because improvement continues during the defense.

POSITIONING THE SQUAD IN THE DEFENSE

The effectiveness of a unit in combat is largely dependent on selecting firing positions that allow the weapons of the unit to be used effectively and to keep the enemy from using their weapons. A primary duty as a platoon commander or squad leader for a rifle platoon is positioning the squads in the defense. When you are employing a squad in the defense, it is good to review your previous experiences as a squad member. Reflect upon the reasons you were positioned as a rifleman, grenadier, or other member of a squad to better determine what type of defensive firing position is needed. There are many points to consider in selecting a firing position. Some of these are as follows:

1. Mission: If the mission of the unit is to defend an airfield, the firing positions of the unit must facilitate the accomplishment of the mission, despite how good other firing positions may be.

2. Enemy: The capabilities of an enemy usually determine how he will attack. Mechanized units usually attack through fields and other open terrain where they can use the speed of their vehicles to an advantage. Infantry units, however, seek to use the cover and concealment provided by woods and other close terrain. Firing positions that are ideal for defending against mechanized units maybe useless for defending against infantry units.

3. Observation and Fields of Fire: Seek to fire on the enemy when he cannot fire on you and do not let the enemy fire on you when you cannot fire on him.

4. Plan of Defense/ Scheme of Maneuver: How the battalion commander plans to use the companies will influence the selection of firing positions. For example, if the battalion commander plans to surprise the enemy, firing positions should be selected that allow the fire of all or most of the weapons can be brought to bear on the enemy simultaneously.

The following paragraphs will discuss what forms a basic defensive firing position.