There are at least two other types of recurring in-jokes that are less obvious to a casual reader. One is the frequent reuse of the name Leigh Hunt for different characters in different novels. Seventeen books have had a character with this name, frequently in the opening prologues, frequently a sailor, usually dying; a notable exception is the first (in chronological order) Dirk Pitt adventure, Pacific Vortex!, in which Admiral Leigh Hunter is a major character, commander of the 101st Recovery Fleet in Hawaii. In the introduction to Arctic Drift, Cussler says there was a real Leigh Hunt who died in 2007 and the novel is dedicated to him. Another is that significant events in several novels occur on July 15 (Cussler's birthday). He also used the name "Periwinkle" in his works. In The Adventures of Vin Fiz (and in other works as well) there appears a donkey named Periwinkle. In Valhalla Rising, the Periwinkle is the name of a catamaran in which Pitt, Giordino, and Misty Graham are rescued by none other than Cussler himself. Cussler's friend Craig Dirgo is mentioned in several books.