How this entire trip came about was when the Captain in Tonga and heard about a local diver who was put in jail for selling bronze items that he claimed were gold.
The police got wind of it and arrested him. Later on the Captain talked to him and discussed plans to dive and excavate the ship wreck. However the police had other plans and arrested him again. They then "breathed heavy" on him to get the location of the ship wreck. The Navy was called upon and paid a ton of money by its own government to grab stuff out of it.
If you are a bit puzzled - google Tonga and you'll find its one of the most corrupt nations in the world. One sobering reason why there are so many ancient shipwrecks there was because the ancient Tongans used to entice the crew of visiting ships onto the island - with girls, feasts, etc.. and massacre them or capture them... and eat them.
Tongans were happy cannibals. They would also place their captives onto an island, using it like a fridge.
Thankfully Christian missionaries converted them and they stopped being cannibals... but not before eating a whole bunch of German missionaries in the process.
The Captain however is an upright dude and has arranged for the proper permits to look for and salvage the wreck.
Meanwhile a whole bunch of local divers were busy pulling stuff out of the sea and trying to sell ancient anchors, bolts, nails, etc.. from sunken ships. The problem with that is - a rusty nail is inherently worthless. Same for a rusty anchor. Or a plate. But if you can prove that the item came from- let's say the Titanic or some other famous ship wreck - and that piece of crap suddenly shoots up in value many many times. The local divers however didn't know how to do this and simply have a pile of rusty shit that no one wants to buy.
The Captain plans to do it properly and try and ascertain the identity of the ship wrecks. Hopefully my education as a historian will help in this approach.