Over the last two years, the insurgents in Iraq, the insurgents - be they Iraqis or part of the Az-Zarqawi-led Al-Qa'idah in Iraq - have learned that they cannot attack American forces directly. Every time they do, they suffer unacceptable losses.
To continue their attacks on the Americans, the insurgents have adopted tactics that allow them to strike without sacrificing themselves. These tactics are in addition to the suicide bombers and the use of their most effective weapon, the improvised explosive device (IED).
One such tactic is the use of a mortar with an improvised delay trigger. Here's how it works.
The insurgents determine as best they can the appropriate firing position of the tube and the suitable charge for the round. The tube is buried or otherwise supported to stand alone. An ice cube is placed in the tube, followed by the round. The mortar team departs the area. After the ice cube melts, the round falls into the tube and is launched at the target.
Why not fire the mortar by hand and run away? They tried that. However, the American military possesses accurate "firefinder" radars, the AN/TPQ-36 and AN/TPQ-37 which can immediately locate enemy fire. The radar back-plots the firing location to friendly artillery and mortar positions to allow for counterbattery fire. Use of this tactic defeats the counterbattery fire.
Another common mortar tactic is to mount the mortar in the back of a pickup truck. The team fires the mortar while slowly moving, which is very inaccurate, or from a fixed position, departing immediately after firing. While counterbattery fire might be effective in this instance, the insurgents normally fire from built up areas - concern for civilian casualties prevents an artillery response.
Although the insurgents can use these tactics to fire mortars, the most effective weapon in the insurgent arsenal is the IED.