I would suggest that this is the last of the war novels, though by the time that this was released the war was almost over (I believe Belgium had been at least partially liberated, and Hitler and the Japanese were on the back foot, though there was still a lot of war to fight at this stage). Most of the album takes place at sea (which is similar to the other war albums) and it noticeably has no antagonist - it is purely a treasure hunt. While the threat of the Bird Brothers still hangs in the background, they do not make an appearance.
This album also brings in the last of the major Tintin characters: Professor Cuthbert Calculus. He appears just after a group of would be treasure hunters (all claiming to be descendants of Red Rackham) appear at Tintin's door wanting a piece of the action. However, Calculus arrives a little later offering use of his submarine. Right from the beginning we discover that while Calculus claims to be 'a little hard of hearing' in reality he has selective hearing, namely he only hears what he wants to hear.
Up until this point most of the scientists that Tintin had encountered have been eccentric, however Calculus, becoming a major character, becomes the eccentric scientist and all of the scientists that appear afterwards tend to be much more level headed. Thus it appears that Herge's quest for an eccentric scientist has come to an end and his cast list is complete.
As mentioned, most of the war albums take place at sea, and this is no exception. Tintin sails off in search of the treasure, and all of the important characters (the Thompson Twins, Captain Haddock, and Calculus) accompany him. This in a way sets the scene for the later books, indicating the characters that will end up playing major roles in the stories. In a way it can be suggested that Red Rackham's Treasure marks the completion of the Tintin world, and now we move on to the other adventures. However, I feel that by this time many of the truly classic adventures lay behind us. However, I am making my way through my collection and will hopefully have a complete set shortly.