It is not ideal, but there is no way to simulate a desigator/missile pairing any other way really. Not without a new game engine.
What about GPS guided rounds? They don't need a designator pairing, you just radio off a string of target co-ordinates over the radio like you would with normal artillery, the only difference is that the shells coming downrange are really really accurate.
I think it could be represented by creating another weapon class which uses the accuracy rating for both direct and indirect fire to represent Excalibur or GMRLS.
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Linka
Summarized
Maybe a third of the guns and rocket launchers [In Iraq] are actually put to work.
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The MLRS has been particularly popular for the last six months, since the new GPS guided rocket became available.
This fall, a GPS guided 155mm shell (the Excalibur) will enter service, giving the M-109s more to do. In most operations, unguided 155mm shells are too inaccurate to use because the fighting is in urban areas. The Excalibur is a different story. The MLRS launchers have used so many GPS guided rockets that these new items are in very short supply, and are rationed.
On the down side, the GPS guided shells and rockets mean that much fewer shells and rockets are needed. It's pretty much, "one target, one shell." With these "smart shells," the number of rounds needed will decline by over 90 percent.