The Assassin by Stephen Coonts

The Assassin - After his son is killed in Iraq, Huntington Winchester and a few of his friends finance a war against terror on their own. They get help from the president in the way of Jake Grafton, retired Admiral and covert CIA employee. His associates begin killing known terrorists, hunting for the big ones, especially Abu Qasim. However, Abu Qasim has an agenda of his own, and when he learns of Winchester’s friends, he goes after that group.