Much is known of what happened during World War 2, but what of the actions of the Axis and Allies in the decade before? The most recent In Focus photography selection answers that question and then some.
Above are three British firemen, fully equipped with gas attack gear during a March 16, 1938 gas invasion drill in Birmingham.
Also note that this selection is the first in a 20-part series running over at the Atlantic, so there's sure to be plenty of WW2 tech, war machines and history coming our way over the next few weeks. [In Focus]