In We Were Soldier, about the Battle of the Ia Drang Valley, artillery and air strikes are routinely called to within feet of friendly soldiers. In Platoon as the base is overrun in the final battle of the film, the Captain requests his air support to drop all his ordinance on top of the base in hopes salvaging the battle. I've also read anecdotes of soldiers calling artillery on themselves during WWII in order to stop an enemy advance, sacrificing themselves in the process.
How close could artillery be brought to friendly forces with creating causalities? Was it ever standard operating procedure to call artillery on top of your position?
One account I can think was the case of John R Fox who called down one on himself in Italy in 1944 when Germans overran his position killing himself and earning himself a medal of honour (which was bestowed in 1997 by Bill Clinton). He is one of the few coloured men so far awarded a medal of honour.
I know of one instance - 18 August 1966 during the Battle of Long Tan. D Company 6 Battalion Royal Australian Regiment effectively walked into an ambush by NVA and VC forces attempting to sneak up on the Australian Task Force base at Nui Dat. During the battle, 11 Platoon was cut off and in danger of being overrun, the platoon sergeant called in an artillery strike on his position which was refused by fire controllers. Instead, artillery was walked in from further out, finally dropping being 50 to 100 metres from the platoon position.
It's perhaps not exactly what you're after, but in this particular instance, and most similar situations, the artillery dropped in will typically be fused for airburst to maximise enemy casualties from shrapnel, and shrapnel doesn't care if you're a target or not.
The Korean War Battle of Kapyong in 1951. Canadian and Australian forces called down artillery on their own positions to avoid being overrun. It worked, the defenders lost around 100 killed and wounded but held while the attacking Chinese lost around 1000 killed and probably many more wounded.
Here's a pretty good doco on it, makes you appreciate how insane all these battles barely anyone knows of were.