U.S. Secretary of Defense Chuck Hagel, center, walks with Mexican Secretariat of National Defense Gen. Salvador Cienfuegos Zepeda, left, and Secretariat of the Mexican Navy Adm. Vidal Francisco Soberon Sanz after the three placed a wreath at the Squadron 201 Memorial in Mexico City April 24, 2014. Hagel traveled to the city to attend the second North American Defense Ministerial conference between Mexico, Canada and the U.S.