Just doing some lazy Saturday browsing, going through the Panerai current catalog, and thought I'd share some of the info here...
From what I can tell, the closest design of the original Rolex Ref 3646 that Panerai sold to the Italian Navy, which you can buy brand new at a dealer today is the PAM1334 Radiomir "3 day":
Here's an original Rolex 3646 from the 40's, with the aluminum dial (they started with plastic but quickly switched to aluminum as the plastic would melt, presumably due to the radiation)
The current Radiomir models only go up to 45mm, while the originals were 47mm
The first Rolex with a crown guard was the Rolex 6152/1 made for the Carabinieri Sommozzatori military division in 1958.
Note that this is also when they started using integrated lugs, rather than wire lugs
This watch is #1 of the series, and
sold at auction in HK for $1m HKD last year (about $125K USD).
They switched to Luminor shortly after that though. Only the first watch in this category is known to use Radiomir. The rest would be labeled "Luminor Panerai" 2 lines only. Later modified Rolexes would also have "Marina Militare". Sometimes they would have both (4 lines)
They don't currently offer a Luminor with 2 lines of printing, so if you don't want a logo instead, 3 lines is as close as you'll get, with the PAM914 (the one I posted a replica of while ago). This has the 8 day movement, which is what the "8 Giorni" label represents.
Here's an interesting one. What was the first non Rolex Panerai watch?
If you include prototypes, that would be the Mare Nostrum chronograph, using an Angelus 215 movement. This 52mm prototype was made in 1955, although Panerai claimed it was 1944 when they started making homages of it, for some reason.
They have released homages to this, but currently there are none listed
The first non prototype "actually Panerai" was made a year later, for the Egyptian Navy, the GPF 2/56. It carries a lot of the design elements familiar with current models in both the dial (with the seconds hand at 9 and the "8 day patented" logo at 3) as well as the rotating bezel. To compete with automatic watches of the 50's, they started using an Angelus table clock movement which could provide 8 days of service. That's the "8 days patented".
Also note this is actually where the crown guard first showed up.
Again, they don't make anything too similar to this one, but any Submersible will have some familiar design elements. They are much smaller, topping out at 47mm while the original was 60mm.
If there's a "quintessential Panerai" look, it would actually be a Submersible with a Radiomir style dial. The cushion case we know and love is a Rolex design. That's why I joke that Panerai is just a Rolex homage company
After that, they stopped selling Rolex in the 60's, Giuseppe died in the 70's, and the company kind of sat around in a stagnant state in terms of watches (they still made military components, but with the end of the Soviet union, this was dying as well) until they popped up again in 1992 and started making homages of their old Rolex designs (and even some homages of the GPF prototypes mentioned above), except in a more modest 44mm size.
The first of these was the Panerai Logo Ref 5218-201/A, using an ETA 6497 movement. This is the watch Stallone "discovered". He sold one of them at auction, saying it's the one he randomly found in Rome. Actually he got 5 of them from Panerai, 4 of them to wear during the filming of Daylight. Those ones were going to be branded "Slytech" but apparently they couldn't switch the dials in time for filming.
Note that it's not a "sandwich dial"
The Richemont version of Panerai has brought out the "Base Logo" model a few times, with and without a sandwich dial. The current one is PAM1086, for $8200 MSRP (original was $1300 in 1993)
Sylvester Stallone "discovered" them shortly after. Actually it was a rep for Richemont (which was a secret at the time) who pitched the watch to Bruce Willis, Arnie and Stallone, and it caught on with the latter. He never did become an actual rep for the company, even though he basically put them on the map. This was their cost though - They developed these watches for him at a time where they could barely afford it. When it came to do an actual launch, he ghosted them. That led to them being very popular, but very broke, and forced to sell to Richemont. His relationship with Richemont seems to have gotten even worse, and you'll rarely if ever see him wearing one anymore (he still wears great watches though, he's often seen with a vintage Daytona)
PS I started this post saying that the closest you can get to the original Rolex today is the PAM1334, but Richemont attempted to get even closer in 1997 with the PAM21. They used movements similar to the original Rolex/Cortebert caliber 618, and on the outside looks like the original Rolex 3646:
They came up with a story that they came across 60 pieces of New Old Stock of these Rolex movements, which upon closer inspection turned out to be false. They are indeed NOS, but they are Cortebert movements made for 1930's pocket watches, not Rolex. Still close as you'll get without buying a 70 year old radioactive watch, but yet another lie from this shitty company who actually have an amazing history. They just choose not to tell it.
*note I am just sort of blurting out stuff from my mind, and this is just a forum post and not a fully researched article!