In the spirit of TMP my recommendations feature no aquatic mammals, vehicles or ships [as far as I know] but are WW2 based so I thought I'd pass them on anyway 
My 11 year old has just been ploughing through books over the summer holidays as part of a pre-high school homework list [homework
in the summer holidays..I ask you!!!]
We suggested he read The Silver Sword by Ian Serrailier which, much to his surprise, he really enjoyed [I don't think he expected anything recommended by his parents to be fun although he's now working through my Terry Pratchett pile].
He has also been planning to read some books by Robert Muchamore, the Henderson's Boys series
link
"Summer, 1940.
Hitler's army is advancing towards Paris, and millions of French civilians are on the run.
Amidst the chaos, two British children are being hunted by German agents.
British spy Charles Henderson tries to reach them first, but he can only do it with the help of a twelve-year-old French orphan.
The British secret service is about to discover that kids working undercover will help to win the war.
For official purposes, these children do not exist."
He hasn't read any of them yet so I don't know the verdict but he did enjoy other books by the same author.