Under a Graveyard Sky — John Ringo

Zombies are real. And we made them. Are "you "prepared for the zombie apocalypse? The Smith family is, with the help of a few marines.

When an airborne "zombie" plague is released, bringing civilization to a grinding halt, the Smith family, Steven, Stacey, Sophia and Faith, take to the Atlantic to avoid the chaos. The plan is to find a safe haven from the anarchy of infected humanity. What they discover, instead, is a sea composed of the tears of survivors and a passion for bringing hope.

For it is up to the Smiths and a small band of Marines to somehow create the refuge that survivors seek in a world of darkness and terror. Now with every continent a holocaust and every ship an abattoir, life is lived beneath a graveyard sky.