I'm in a squad level game at the moment and it really, really sucks not having fire support.
I heartily endorse everyone to get their PCs to get at least a 60mm mortar. At worst, there's several breeds of 51mm ('commando') mortar out there that can bring down devastating fire on the enemy.
Now, you may be thinking 'Pah! My M203 grenade launcher, backed by it's big brother the Mk 19, can deal with anything!'
The difference in explosive power between a grenade and a mortar bomb is immense.
These are the 40mm HEDP and the 60mm HE.
The big problem with mortars is their minimum zone, with the above bomb you are looking at 70m, vs the 10m for a launched grenade.