The Panerai were originally designed for the Italian military as a dive watch (hence the lockdown crown guard). They are large, very large, watches typically in the 44mm range and their popularity among certain celebrities (Stallone, Hugh Grant, Ewan McGregor, Jay Leno) have made them a pretty hot item over the past several years in the watch world. They use what is essentially a small pocket watch movement (Unitas) which is one reason the small second hand is at the 9:00 position (think pocket watch with the stem at 12 and the seconds at 6).
Most people have a love em/hate em relationship with the Panerai, but it is an interesting design, with historical significance, as well as something of a fashion statement.