Forces under John J. Pershing cross into Mexico.

A U.S. Army expeditionary force under the command of John J. Pershing crossed into Mexico.

 Pershing in Mexico some days later.

The force was made up of 4,800 men from the 7th, 10th, and 13th Cavalry, 6th Field Artillery, the 6th and 16th Regiments of Infantry, the 1st Aero Squadron, and support personnel, with that force divided into two columns.  The western column entered Mexico from Culberson's Ranch New Mexico, entering Mexico at midnight and marching 50 miles that day to Colnia Duban.  A march of that rate remains a significant advance for an army on the march and in 1916, when the primary means of transportation was foot leather and the horse, that was a really remarkable march.

The second column crossed the borders south of Columbus with there being some legitimate fear that it might immediately encounter Carranaza's forces in hostile resistance.  In the days since the Columbus Raid Carranza had reluctantly entered into an agreement allowing U.S. forces to operate in Mexico against Villa, but the agreement was a reluctant one and it was not clear if Mexican forces would honor it.  The column technically entered at noon, but in fact entered some hours earlier.