All along I had the SBBN007 "Tuna" Professional 300m. I was lucky to have bought one of the last pieces back then from Seiya Japan when the SBBN007 was discontinued.
But a true Tuna, in my eyes, should have a black bezel insert. This got me looking at the SBBN015 Marinemaster 300m which is also powered by the 7C46 7-jewels high torque quartz caliber. The price of new SBBN015 is on the high side and I was lucky that "AL" in Hong Kong has a mint piece on bracelet up for sale, I grabbed it.
The first thing I did was to swap the bracelet with the rubber: SBBN015 having the classic old-school look and SBBN007 with the cold "All-Steel" look.
The SBBN015 has a signed crown and hex-screws.
The original bracelet is one hell-piece of steel with double locking clasp and divers' wetsuit extension.
"Titanium + Stainless Steel" - This guy means business!