Crusade is the second book of the Destroyermen series. MatthewReddy, and the crew of USS Walker (DD-163), are reunited with the destroyer USS Mahan (DD-102), and set out to fight the Grik. Reddy and Walker's marine detachment, continue training the Lemurians to defend themselves and take the war to the Grik. The Grik have now taken over the ship that was chasing them, the Japanese battlecruiser Amagi.