Al Qaeda is a militant Sunni Muslim organization dedicated to wiping out all Western influence in the Middle East. Its credo is that Judeo-Christian nations are bent on destroying Islam and must be stopped. Branded a terrorist group by the United Nations, al Qaeda—formed in 1988 by Islamist Osama bin Laden—is believed responsible for the 9/11 attacks on US territory, and its Iraqi contingent fought against NATO coalition forces in Iraq, including during the Battle of Ramadi in 2006. Al Qaeda commanded the mujahideen, the chief military units arrayed against the authors’ SEAL teams during their time in Iraq.

Three types of armored vehicles recur in the book. In the book, they’re used by Army units either to push into enemy territory or to defend and/or rescue SEAL teams when they get into jams. These vehicles aren’t critical to the story or the lessons, but they crop up frequently in battle scenes, often enough to become terms of interest.

The biggest vehicle used in Ramadi is the Abrams M1 tank, since 1980 the artillery mainstay of the Army and Marines. It fires a shell nearly five inches wide, “bring[ing] the thunder” (19) to bear on the enemy. An Abrams tank can knock down walls, blow up enemy gun nests, and generally destroy things in its path.