Anti submarine devices have been around for a while. Some time ago, they usually looked like a package shelf below the dashboard. The Idea was that your knees would hit the device if you slid forward in a crash.

There are several hits on google that explain that these seats have special shaping in the front of the seat to keep you from sliding under the dash.

If you view this video -

http://www.youtube.com/watch?v=O95XXvr7-m0

You can not really see much that is special about the seat fronts, but I think that the dash is very deep, below the level of one's knees.
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'96 855R,'64 PV544 driver, '67 P1800 basket case, '95 855, '95 854, the first three are mine, heh, heh, 485,000 miles put on 9 bricks