WASHINGTON — Since President Obama took office, the Pentagon has transferred to police departments tens of thousands of machine guns; nearly 200,000 ammunition magazines; thousands of pieces of camouflage and night-vision equipment; and hundreds of silencers, armored cars and aircraft.

In May, The New York Times requested and received from the Pentagon its database of transfers since 2006. The data underpinned an article in June and helped inform coverage of the police response this month in Ferguson, Mo., after an officer shot Michael Brown, an unarmed teenager.