John Mosby brought up some good points about getting close to an enemy force negates some of their IDF capabilities. This is true, it is a tactic that the PLA used quite effectively in Korea and was used by the NVA/VC to negate American IDF in Vietnam. This isn't a tactic that the insurgents in Afghanistan or Iraq have used very much, although it remains a valid technique, John also pointed out that even with dismal marksmanship training most Americans are good 200 meters and under which may explain why the Iraq/Afghan insurgents don't use this technique.
Indirect fire is the "Big Hammer" on the battlefield. Indirect fire comes from mortars, cannon artillery, rocket artillery, close combat aviation (helicopters), and close air support (fixed wing).
Mortars. Mortars are a "high angle of attack" platform controlled by the ground maneuver commander (Platoon level in the USMC, Company level in the Army). High angle of attack means the tube is angled between 45 and 90 degrees. Mortars are the quickest IDF to respond to enemy contact. The effects of mortars depends on the size of the round, a 60mm mortar is barely better than a hand grenade, an 81/82mm mortar is about 50% again as effective, and a 120mm mortar is about twice as effective with a ground impact fuze. With an airburst proximity fuze they are a bit more effective. Time of flight can be anywhere from a few seconds up towards a minute (or longer for some heavy mortars).
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