REVERSE SLOPE DEFENSE
"In battle, casualties vary directly with the time you are exposed to effective fire. . . A pint of sweat will save a gallon of blood."
A reverse slope defense is a positioning technique characterized by the location of defensive forces on a slope of a hill, ridge, or mountain that descends away from the enemy. It is one of several time tested techniques that may be used as part or all of a unit defense.
The reverse slope defense protects the infantryman from enemy long-range direct and indirect fires.
WW II: JAPANESE DEFENSES ON THE PHILIPPINES- -THE 6TH ID
Reverse slope defenses were more often used by enemy forces in WW II and Korea than by U.S. units. During operations on Luzon in the Philippines (July 1945), the 6th Infantry Division discovered how the Japanese used such defenses to good effect. From 3-8 July the soldiers of the 6th ID tried to take a well-fortified position along what was called Lane's Ridge. The position was only assailable from the front since each flank was protected by dense thickets on one side and a deep gorge on the other. These frontal attacks got nowhere until on 7 July, after extensive air strikes (including napalm) and artillery barrages, the 6th managed to take the forward slope of the ridge. However, trying to continue the advance, the soldiers discovered that the Japanese had also fortified the reverse slope with 55 emplacements including 13 pillboxes. Once again artillery was called in, including shells using the new VT fuses. Under the cover of a smoke screen and with quad .50 caliber machine guns blazing, the men of the 6th Division stormed those positions on 8 July, but at heavy cost. The reverse slope defenses, unexpected and virtually impervious to observed artillery fire, proved to be more costly to take than forward slope positions. 
A reverse slope defense is especially useful when the light infantryman finds himself on terrain which is exposed to enemy long range fire systems.
90TH ID: C CO ON THE FORWARD SLOPE
A clear example of the dangers of placing your men in an exposed position was the poor placement of C Company of the 1st Battalion/357th Infantry of the 90th Division in WW II. Then MAJ William DePuy, the battalion commander, recounts this story:
"When we got up between the Prum and Kill Rivers [Germany, 1945], we encountered a very high open ridge. One of my company commanders put his 'C' Company out in the snow on a bare forward slope. They dug in and everyplace they dug they made dark doughnuts in the snow. On the other side of the river there was another ridge. On top of that ridge were some German assault guns, and they waited until the company commander had all of his troopers scattered around in their foxholes on the forward slope, and then, they just started firing with their two assault guns. It was murder. Finally, after they killed and wounded maybe 20 men in that company, the rest of them just got up and bolted out of there and went over to the reverse slope, which is where they belonged in the first place. So, being on a forward slope when the enemy has direct fire weapons, high velocity direct fire weapons, is suicide." 
KOREA: "FRONT LIGHT, REAR HEAVY"
The Chinese Army in Korea greatly feared and respected the volume and accuracy of U.S. artillery fire and air strikes. In a captured Chinese report on their "lesson learned" after battles with the U.S., they said, "the enemy [U.S.] has stronger artillery than we." As a result, the Chinese decided to put their forces, "front light, rear heavy." That is, they put a few reconnaissance troops on the forward slope of the hill while putting most of their troops on the reverse slope. They were placed "in well-protected holes dispersed over the crest of the hill from where one can easily push forward." These units achieved the maximum protection from the deadly effects of direct and indirect fire weapons at a minimum loss in defensive power. When facing an enemy rich in artillery and air power, the reverse slope defense proved a good bet for the Chinese. 
The reverse slope defense brings the battle into the range of infantry weapons.
Argentine defensive positions in the Falklands were normally located on the forward slopes. This permitted the British forces to observe and accurately locate the Argentine positions. They then would direct accurate artillery fire and antitank guided missiles into those exposed positions. The Argentines were driven out of their holes by this concentrated fire. The British were quick to capitalize on the vacated positions. When 2nd Battalion, the Parachute Regiment (2 Para) took Wireless Ridge, they occupied the vacated Argentine positions, now on a reverse slope from the enemy. From those positions the British were protected from Argentine artillery fire. The Argentines were not able to place effective artillery fire over the crest of the mountain. 
Positions on the reverse slope are hidden from enemy observation and can hide your strength and locations.
Reverse slope defenses would also have been better than a forward slope defense at Darwin Hill and Boca House where the British again used MILAN ATGMs to destroy Argentine forward positions one by one. British sources indicate that had the Argentines adopted reverse slope defensive positions with observation posts (OPs) on the forward slope, they would have been denied the British detailed knowledge of their defensive positions. 
FM 7-20, The Infantry Battalion, Dec 84. Chapter 5, gives the advantages, limitations, and organization of reverse slope defense.
FM 7-22, Light Infantry Battalion, Mar 87. Chapter 4, Section V, gives the concept, integration, organization and a scenario for a reverse slope defense.
FM 7-71, Light Infantry Company, Aug 87.
The Combat Studies Institute Research Survey #6, A Historical Perspective on Light Infantry, Sep 87, provides an excellent discussion and graphics of the reverse slope defense used by the CHICOM in Korea.
The reverse slope defense can (depending on METT-T) provide a critical "edge" to the light fighter on the firepower intensive battlefield.
A Sample Company Reverse Slope Position
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