I know a few people who have had to do just that in hard clay soils, sometimes making as many as 3 good passes to get the desired depth. I suppose it could even take more passes, depending on just how compact and dry.
A subsoiler, as pointed out, can really drag the rear end down into the dirt, but just experimenting with the top link/angle, you'll get the hang of it. I've even heard the suggestion that one water the area well for a few hours before beginning to help the sub soiler out a little.
I have sandy soil, so I don't have the problem here.
John