Sailly-le-Sec (French pronunciation: [saji lə sɛk]; Picard: Sailly-Sé) is a commune in the Somme department in Hauts-de-France in northern France.

The commune is situated some 13 miles (21 km) east of Amiens, by the banks of the river Somme, on the D233 road.

On the night of August 8–9, 1918, as three Battalions of Doughboys from the 33rd U.S. Infantry Division were joining the Allied offensive during the Battle of Amiens, American war poet Lieut.

Thomas J. Cochrane were assigned to deliver sealed orders from Division HQ at Molliens-au-Bois to the Field Headquarters of all three Battalions engaged in the attack.

The location of each Battalion was unknown, but they were believed to be along the northern bank of the Somme River, near the village of Sailly-le-Sec.