in 2002 (E series) Panerai introduced an upgraded movement for the historic line of manual winds. It was still based on the ETA 6497, but had redesigned bridges, a swan-neck regulator and increased power reserve (56h instead of 41h). In 2005 (H series) there was another redesign of the bridge decoration to the much nicer CTG of today. The 249 and the 232 saw the current movement used in all the historic line (with the exception of the introduction level PAM zero and 5 that have the old pre-E movement behind the solid caseback and also the new PAM 26 SE introduced this year).
In the 1930'-50's where the Rolex base caliber (618) was used in Panerai, the swan neck would have been too expensive for these military watches. There were very nice variations of the Rolex movement used in fine pocket watches that had regulators.
Hope it helps,
Asi